More Plating Tips for Plastic Injection Molded Parts

There are many, many plating tips and secrets of the trade that one learns throughout the years.  You may have heard some of these, but following are a few key pointers to keep in mind.  They could save you a lot of time and aggravation down the road.

Avoid using chrome when molding with polyvinylchloride (PVC).  Chloride is a component used to strip chrome off of steel; therefore the chrome will slowly dissolve due to the gases emitted from the chloride in the PVC.  There is an old school of thought that chrome is better than nickel.  Don’t believe it in this case.

Polytetrofluoroethylene, or PTFE, breaks down at 550xF.  If you are using a molding application requiring mold temperatures that exceed this level, avoid PTFE and go with nickel or chrome.  The PTFE, though useful for release, will break down and shut you down. It is not a bad idea to occasionally use different combinations of plating.  Depending on what kind of performance you require from your mold, consider having more than one plating material for optimum efficiency.  For example, if you require abrasion and corrosion protection, a base layer of electroless nickel (for corrosion) and a top layer of hard chrome (for abrasion) are recommended.  The two work together very well.

Technology now allows us to skillfully and effectively mask off even the most remote areas of a mold so that very localized plating can be applied.  Selective plating with electroless nickel, for example, is a great way to correct size on threaded cores or slides for ring necks threads.  This application is good for corrections under .004 inch per side. Need just abrasion protection?  Go for hard chrome with a heavy flash of between .0004 and .0006 inch – especially if you are using glass-filled materials.

If corrosion protection is needed, an electroless nickel .0002 to .0004 inch deposit is an excellent choice.  If corrosion protection and release is needed, a co-deposit of electroless nickel and PTFE – 25 percent by volume – is a proven combination.

When selecting electroless nickel for rubber molding, we have seen sulfur-cured materials still unwilling to release, so a heavy topcoat of PTFE is usually required.

An effective use for chrome is shimming or correcting for size on inserts, cavities and cores.  You can mask and selectively plate the parts up to a .020 inch deposit, finishing it with either grinding or EDM.

As always, when choosing plating you need to know what type of steel grade and what plastic material will be molded.  Communicate these details to your experienced plating house and, based on your molding requirements, you will have the ultimate finish on your molding surfaces, saving you time and money and producing the high quality parts your customer expects.

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Polishing Pointers-Saving Time On Ribs

Ask most shop owners what the number one reason is for new molds failing their first sample and you will most likely hear “material sticking in the ribs.” It is not uncommon for a tool to have its ribs and slots repolished two, three or more times before the tool works cleanly. The following is a list of different polishing techniques along with the pros and cons of each – and some tips and secrets to not only cut polishing time, but ensure a smooth-running tool every time.

The Problem

EDM is the primary reason material sticks in ribs. Not only can the surface be extremely rough, its hardness (the white coat) ranges about 72 Rockwell due to the combination of heat, oil and carbon – which are primary elements of heat treating steel. The combination of surface hardness and roughness leads to long hours of polishing, which despite the polisher’s best efforts, may still result in a poor performing tool. Undercut ribs due to cutter flexing also is an issue, but this article will deal solely with EDM-related problems and its solutions.

Disking

The technique of disking ribs is probably the fastest way to remove EDM from ribs; however, the downside can easily outweigh the benefits. Disked ribs can become undercut extremely easily – in a matter of only a second – and this technique should only be used by an experienced polisher with many years of “feeling with his fingers” – or discarding the block and starting all over again is a real possibility. Young and inexperienced polishers – often intent with impressing the owner with their great speed and who are totally ignorant of the severe consequences possible – are the least qualified people to use this technique, but are often the first to do so. Ironically, the older, more experienced polishers – who are the most capable of handling this technique – are the least eager to use it because of well-founded concerns about damaging the block. They opt to use other slightly slower, but safer methods.
Several methods of disking ribs include:

Putting a two- or three-inch disk in a one-inch disk holder and reaching down into the rib.

Tearing off the attached center mount from a disk and then backing up the disk with a homemade thin steel disk, while using a cut-off wheel arbor to hold it all together. This allows both increased depth and pressure to be applied to the disk at once.

Cutting an extra-large diameter steel disk from a sheet of galvanized steel -as in duct-working material – and mounting this disk onto a quarter-inch screw, then adding sticky-back strips of abrasives all along the cutting surfaces. These strips are easily replaced when they become worn out and allow for the disking of extremely deep ribs.

If disking is your choice, please be careful to leave 10 percent of the EDM on all of the surfaces to guarantee no damage to draft angles or the thickness of the rib.

Diamond Files

Diamond files are the next fastest cutting tools available for removing EDM from ribs after disking. Diamond files can be used in profilers, heavy-duty air profilers and by hand. One advantage is that the diamond’s hardness is ideal for cutting through EDM’s outer surface. Unfortunately, the cost of diamond files can be prohibitive – especially on larger jobs, which may require dozens of such files. Unwary polishers also have destroyed these files carelessly by pushing down on them too hard. They think that pressure makes them cut faster when in reality they were simply breaking the diamond particles off of the file. By embedding the particles into the steel they were exceeding the limits of the braze that holds the diamond onto the file – resulting only in stripping the file clean and wasted time and money. The ultimate tool would be something that stays sharp forever and holds diamond without the particles breaking off.

Steel Laps

Steel laps are the tool of choice for most polishers. Steel can be ground to any thinness and still allow for heavy downward pressure. Steel laps can be used with diamond compound or silicon carbide lapping compound as the cutting medium. Lapping compound is only slightly slower than diamond, but considerably cheaper. Unfortunately, the downside to steel laps is greater than the benefits derived from them – steel laps often create deep, “zig-zag” lines in the side walls of the ribs, which are often far worse than the EDM with which they started. This is due to “scoring” between the steel rib wall and the steel lap. The only way to get around this uncontrolled scoring is to not push down so hard, but this also slows down the cutting process. Another big disadvantage to steel laps is the combination of downward pressure and the cutting action of the profiler, which often causes the diamond or lapping compound particle to simply shatter into fine grains. Shattering the rough grain and leaving a fine grain wastes time. The ultimate tool would allow downward pressure without shattering the larger size grains.

Two examples of steel laps are:

Pre-hard rod cut to thickness and length.
Stainless steel butter knives are often already the perfect thickness, blade length and strength for deep rib work and are the ideal width for mounting sticky-back, press-on paper abrasives. They also can be mounted into profilers and heavy-duty air profilers.

Brass Laps

Brass laps also are very popular for lapping ribs. While not quite as rigid as steel laps, brass laps are easier to work to thickness and shape and they don’t suffer nearly as much from the deep, zigzag scoring as steel laps do. Overall, brass laps may be the most finish control-orientated lap being used. The downside is the large grains of diamond and lapping compound are still shattering from the pressure and cutting action of the profiler, which results in slower times to finish.

Copper Laps

Although copper laps are hardly ever used, they are extremely valuable to the polisher. Their use offers a great improvement in time saved while polishing ribs. This is due to the softness of the copper itself. Copper laps are so soft that the rough grain of diamond or lapping compound never breaks into fine particles. Instead, the large particles embed themselves into the soft copper and become a truly aggressive cutting tool – causing more wear to the EDM than any other form of lap. Unfortunately, copper is so soft that dressing it down thinly enough for most ribs takes all of the strength out of the lap itself – making it practically useless except for the widest and shallowest of ribs. Whenever possible, copper laps should be used as a great timesaver.

Stones

Nothing else cuts EDM faster and has a more controllable finish than a stone. While diamond files start off as being faster than stones, they quickly wear down from use and do not replenish their cutting action with new layers underneath as stones do. The fastest of all stones is a medium, hard-bond, aluminum oxide, nonoil-filled, 220-grit stone. This type of stone, when used properly, is EDM’s worst nightmare. The secret to proper use is to cut it to thinness, dress it with 220-grit (mesh) natural diamond and stone by hand with a side-to-side sweeping motion – exactly like a windshield wiper on a car. This action will tear EDM out of a rib faster than any other method and allow the polisher to maintain total control over the final finish. The downside is that all stones break very easily when dressed down this thin. The cutting action is phenomenal, but when pressure is applied the stone always snaps off. The only thing this combination needs is the strength of steel or brass to become the ultimate rib polishing tool.

The Ultimate Rib Polishing Tool

Take a brass lap, dress it to half the thinness of the rib, take a 220-grit, medium, hard-bond, aluminum oxide, nonoil-filled stone and slice it to half the thinness of the rib. Then smooth off the tip of the brass lap, apply a drop of ethyl cyanoacrylate glue (instant nail glue available at any drug store) and glue the slice of stone directly to the lap. Wait about a minute, then apply just enough 220-grit natural diamond compound to impregnate the pores of the stone and start the sweeping action on the EDM – you are now using the ultimate rib polishing tool.

This combination offers the following benefits:

It accelerates controlled EDM stock removal like no other motion or technique.

The 220-grit diamond is not shattering at all because it’s embedded safely in the pores of the stone.

The diamond compound remains aggressive until it is completely worn out and then is easily refreshed by applying just enough compound so as to refill the pores in the stone.

It also may be used as “draw” in a profiler, but side-to-side sweeping is much faster; therefore, draw should only be used to finish and not to rough out.

The fact that the 220-grit diamond particles fall so neatly into the pores of the 220-grit stone creates nothing less than a “super” diamond file, which is glued to a brass lap that is unbreakable and will never wear out.

When the stone slice wears out, simply glue another one back on and you have a brand-new, super diamond file.

One five-gram tube of 220-grit (mesh) natural diamond applied properly is enough to easily polish all of the ribs most shops produce in six months or more.

Gluing a piece of stone onto a brass lap, charging it with natural diamond and using it in a sweeping side-to-side motion is nothing more than taking the best parts of several different techniques. This solution has worked very well over the years and has cut rib polishing time on some jobs by as much as 50 percent or more – without risking rib damage.

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How to Stay Competitive in Mold Market

At a recent Society of the Plastics Industry (SPI) meeting held in California, three experienced industry experts led a seminar called Moldmaking on a Global Scale to an audience of more than 80 moldmakers. Each brought with them a wealth of knowledge from real-world experience, and shared their expertise on how to position your company and compete with foreign competition through buying and selling molds overseas. A comparison of Asian technology and training to U.S. capabilities also was discussed. Following are the highlights of the presentation.

Purchasing Work From Overseas

According to Larry Courter,  the most important thing to remember is not to look at China and other foreign countries as a threat. Instead, they should be viewed as resources that can help you satisfy your customers’ needs by building certain types of molds. It’s a way to enhance your business, not take away your business.

Courter explains that the first thing you need to possess to purchase molds from overseas is an understanding of the companies with which you wish to work. “You must be sure that you are very specific with the information that is given to them in concise quotation form – accurate data and complete prints or CAD data with notes and QC specifications,” he states. “All of these issues are critical when dealing offshore because communication is not only a matter of distance; it also is a matter of a language barrier.”

So, from a standpoint of CAD data, prints and quality plans, the request for quotation has to be very specific while spelling out all of the components and the construction method to which you expect to have the tool built. Once that is fully understood, they can develop an actual quotation.

“I’ve spent more than 10 years dealing with China and I believe that companies there are – in most cases – very trustworthy,” Courter comments. “The owners pride themselves on their reputation and work. Remember, though, that there are different classifications and levels of competency, so if you go to China and do a complete survey of a company, check out what their customers have to say. You can’t just drive around and look for moldmakers to do business with. You also must respect the culture and understand that you need to spend time developing a relationship with the company that you choose.”

Another word of advice is not to make a decision just based on price, Courter cautions. “Too many companies go to China with the thought that they are going to lose their current customers if they don’t get a cheap mold,” he says, “so they look for the cheapest mold, instead of high value on what they are purchasing.

“There are certain kinds of molds that you should not get built in China – typically the higher cavitation molds,” he continues. “China does a tremendous job with one-, two- or four-cavity molds. It just doesn’t have the technology yet for high cavitation with high precision and they will be the first to admit it.”

Asia vs. the U.S. – Training and Capabilities

“Education- and training-wise, Hong Kong has a great facility and Singapore has a simply amazing facility where they train 3,000 toolmakers a year,” says Glen Shrigley, general manager for the plastic injection tooling division of Trend Technologies (San Jose, CA) – a tooling provider which specializes in computer enclosure parts as well as automotive and consumer products. “The way it’s outfitted and funded just blows away anything that we have here in the U.S.”

Shrigley believes that Asia has really developed its next generation of moldmakers, while here in the U.S. – at least on the west coast – there isn’t much going into apprenticeship programs, which is the main reason he joined SPI.

“I wanted to try and help do something about it,” he says. “We train our own apprentices here and in the last six years we’ve had five people graduate from a four-year apprenticeship program – not very comparable to 3,000 a year!”

The focus that the Asians have regarding this topic is pretty amazing, according to Shrigley. In Hong Kong, they established the Hong Kong Mould and Die Council, where business owners meet as an industry group and set standards, rather than do things on an individual basis. “I was very impressed with their focus on manufacturing, compared to the U.S. where fewer people are getting into the trade,” he states. “When I talk to young people about apprenticeships, I hear that they don’t want to build molds or get into machining – it’s not glamorous enough. We need to start recruiting at an earlier age like they do in Asia.”

Asian facilities also receive industry support from different vendors supplying machines, equipment and software for free. According to Shrigley, a major software manufacturer donated 75 seats of its software to the institute. They knew that if they trained students on their software, it would become the predominant software in the industry and businesses would buy it, he notes.

“Asia has the exact same equipment and capabilities that we do, but they are more focused on their work,” Shrigley comments. “They get us with the pricing because their wages are lower, so we have to improve our delivery times. We can compete by doing a high quality tool faster than anybody else does. And while we use the latest technology, U.S. moldmakers usually don’t share this technology with other shops. They figure that this is their competitive edge, but in reality this makes our industry weaker as a whole because there’s not enough people learning it. In Asia, when new technology is developed, they share it.

“I’m not worried about foreign technology today, I’m worried about their technology during the next five years because they’re training their next generation of toolmakers much better than we are here,” he adds. “Unless we start doing something here and the various associations and shop owners get together and start developing our future toolmakers, this industry will be in trouble.”

Marketing and Selling Overseas

Jim Meinert, director of international marketing for Snider Mold (Mequon, WI) – which builds large compression, injection, RIM and structural foam molds – has been selling molds overseas for about 30 years and it comprises about 30 percent of his business. “Speaking from my own experience, we made sure that we differentiated ourselves by size, type of work, location and time compression,” he explains. “You have to be relentless. I recommend going vertical – product design, prototyping, etc. – to get more work and provide a full service, not just mold building. If you do something really well and something different, you can compete against imports and exports better. Find your niche and market it aggressively.”

Luckily, Meinert says the plastics industry is still in a growth pattern. For example, some data from SPI shows that plastics has grown at a very nice compound rate of about four or five percent throughout the past quarter of a century, while all other manufacturing has grown at only one or two percent because so much of it has moved offshore. “You just need to carve out your niche in this growth industry and realize that it’s all about change,” he notes.

“There’s a book that’s been at the top of the best selling books lists – Who Moved My Cheese? – that talks about change,” Meinert says. “It’s really important for this industry to quit doing things as it normally does and do something different. If you keep things the same, you are not going to get anywhere.

“You also need to follow your customers,” he continues. “For example, General Motors opened up a new plant in Brazil, and it had approximately 18 suppliers move right next to them for support. It’s hard for a small moldmaker – the average moldmaking company is 20 to 25 people – to do that by itself, but I think moldmakers need to partner up to make this happen. It’s just starting to happen in Mexico.”

Meinert also stresses the importance of building valuable relationships with overseas companies. He has a relationship with a gentleman who is the head of a plastics research institute in China and he tells Meinert what’s going on, what kind of plastics they are using, what processes they are using, etc. This information has been vital to Snider Mold’s success.

In conclusion, he offers the following advice. “The key is early involvement with product design,” he states. “We’ve been going 24/7 for quite awhile at Snider Mold just to keep things moving quickly. We’ve built molds in as few as 10 days when we’ve had to. Embrace change, deal with change. You just have to be at the top of your game now. Years ago there was a little room for latitude, but today that is not the case.”

P20,A Good Choice for Mold Steel

P20, a 4130, 4135 modified material, has long been the steel of choice for pre-hardened mold steels. P20 is classified as a chrome-moly alloy, with a carbon content of approximately 0.30 to 0.40. Over time, many variations on basic P20 chemistry have been introduced to the marketplace. Each modification can have an effect on the various processes used in the fabrication of a mold.
Types of Material
The moldmaking industry in the U.S. is Eurocentric in nature. European immigrants came to the U.S. with trade backgrounds and had a large influence on the mold building industry. They naturally gravitated to building molds with the chrome-moly steels they were used to, such as DIN 1.2311 and DIN 1.2312, or their close cousin, AISI P20.
P20 differs from region to region in the worldwide market. Europeans generally use the DIN spec materials (1.2311 and 1.2312), while in Japan, PX5 is the new standard P20. The Chinese market is less clear, because the lack of information about the materials being used for their molds makes it difficult for secondary polishing and texturing processors to know what they are dealing with. The U.S. market is a melting pot of different grades; Figure 1 shows a chemical breakdown of the materials used in the U.S. As the figure illustrates, there are variances within the P20 family, and depending on the steel supplier, an order for P20 could be filled with nearly any one of them. Two of the items listed in the table (P20 premium and high hard P20) are actually closer in chemistry to a 4340 material, which is a chrome-nickel-moly material. As noted earlier, P20 is in the 4130, 4135, 4140 (chrome-moly) family.
These variations can affect costs and time for secondary processors. Most moldmakers look at two key issues when purchasing P20—machineability and stability. If the chemistry of the material lends itself to the formation of hard spots (carbide segregation), it can be much more difficult to machine. Machining cost can account for 50 percent or more of the cost of building a mold, so any increase in machining time can be expensive. Hard spots also cause reduced cutter and insert life, which will also increase costs. If the chemistry does not minimize hardness drop-off from the surface of the block to the center, it will cause increased stress in the steel. When the stress is relieved by machining away mass, the block will warp or twist out of shape, making it necessary to remove the steel from the machine at various intermediate stages and send the block out for thermal stress-relieving. The result is increased cost and lost leadtime.
Surface Finish
Once a mold leaves a shop, it usually requires a specific surface finish to be applied—polish, texture or EDM finish. The quality of the P20 being used can affect each aspect. Four factors determine the quality of the surface finish of P20 steels1:

Percentage of Content

The number of elements added affects how a material polishes or textures. For example, the sulfur content determines how well a P20 polishes. The higher the content, the more difficult it is to get a mirror finish. Sulfides tend to erode or be pulled out of the surface during the polishing process, resulting in a pitted surface. Most P20s will polish to a good #2 finish. The best P20 in terms of polishability is probably #3 steel, due to its extremely low sulfur content. However, low sulfur content reduces machineability.

Homogeneous Distribution of the Alloying Elements

P20 is iron combined with alloying elements. How these elements are distributed within the matrix of the steel is very important. If the distribution is not even throughout the steel, pockets will form, leading to voids, hard spots, soft spots or other imperfections. Correcting these areas will add cost.

Hardness Distribution

P20 is textured by using an acid to eat away the material. If the hardness of P20 is not consistent throughout the mold, the texture depth on the surface will vary. This can be a major problem in large blocks of P20 because of differences in hardness from surface to cores.

Welding

One of the greatest concerns when texturing P20 is welds that might be in the mold. The HAZ (heat-affected zone) around the weld can be 15 or more points of HRC higher than the base metal. With the base material hardness of 28/32 HRC and the HAZ being 15 points higher, the difference in texture depth between the two areas can be as great as 50 to 60 percent. This will cause a halo effect on the textured part and increase the gloss factor, which will increase the amount of handwork required to complete the textured surface, again resulting in higher cost and lost leadtime.

The alloy content of the variations of P20 also affects the welding process. The higher the steel’s alloy content, the more susceptible it is to cracking. Many high-quality P20 versions from Asia (mainly Japan) have lower carbon contents and commensurately higher toughness. It is unusual for cracking to occur in these steels. The lower carbon content also keeps the hardness rise of the HAZ to just a few points. As the carbon content and the content of other alloys (such as nickel) are increased through the standard P20s and some of the high hard P20s—as well as on some of the DIN spec materials—pre- and post-heating becomes critical to controlling cracking and extreme hardness rise in the HAZ. This can add time and cost to the welding process.2
Making a Decision
Extreme pressure is being applied to leading steel producers in the U.S., Europe and Japan to develop new, advanced grades of mold steels. New melt and refining technologies, alloys and free machining additives are, or will be, available to moldmakers. The new steels these pro-ducers develop, properly used, will allow moldmakers to be the best and most competitive in the world.
Until then, U.S. moldmakers will continue to use P20 because they under-stand the basic problems associated with the grade, and although it is costly, they can overcome those problems. It is like fighting with an old friend. However, moldmakers must keep in mind that overcoming most P20 problems requires that extra time and cost be built into the job. In this cost-reducing, leadtime-reducing world economy, to be competitive moldmakers must eliminate these prob-lems by looking at key issues that affect delivery and cost when purchasing variants of P20.