mold design

Plastic Injection Mold Design Guidelines in 2017

Designing Your Plastic Part

When designing parts for injection molding, the manufacturing process is an important consideration. Injection molding is a process in which solid thermoplastic resin pellets are melted, injected into a mold, and then cooled back to a solid state in a new form. During Boss both the injection and cooling stages of the manufacturing process, there are several factors that may affect the quality of the final product and the repeatability of the custom mold manufacturing process. Although it is not always possible to follow all recommendations, outlined on the following pages are some of the most fundamental guidelines when designing parts for injection molding.


An inside radius should be at least 50 percent of the nominal wall thickness. An outside radius should be the nominal wall thickness plus the inside radius (150 percent of nominal wall). Sharp corners at the base of bosses and ribs can be stress concentrators. The edge where a boss meets the nominal wall should be radiused to reduce the sharp corner without increasing the wall thickness enough that it creates a sink problem. The radius at the base of a boss should be ¼ of the nominal wall with a minimum radius of 0.015”.



Design Recommendations:

Wall Thickness

  • Maintain a wall thickness of less than 5mm because thick walls can lead to long cycle times and poor mechanical


  • Avoid large variations in wall thicknesses in order to simplify flow pattern and minimize variations in shrinkage that can lead to warpage.
  • Avoid abrupt changes in wall thickness, as this can create stress concentration areas that may reduce a part’s impact strength. Wall thickness changes should have transition zones that reduce the possibility of stress concentrations, sinks, voids, and warp.
  • Avoid gating near an area with a large variation in wall thickness because hesitation and race tracking can create non-uniform flow and shrinkage.



  • Maximum rib thickness should be 0.5 to 0.75 of the nominal wall to avoid creating areas of sink.
  • To avoid thin sections of steel in your mold, the distance between ribs should be at least two and a half times the nominal wall thickness.
  • Ribs should have a draft angle of at least ½˚ per side in order to accommodate easier ejection from the mold.
  • Maximum rib height should be no greater than three times the nominal wall thickness in order to avoid large variations in wall thickness.
  • Balance ribs on both sides of the nominal wall to avoid non-uniform shrink that can lead to warpage.



  • Stand-alone bosses should be designed following the design guidelines for ribs

(see more information under the “Ribs” section).

  • Use connecting ribs and/or supporting gussets if possible to stiffen structural parts. Connecting ribs should be 0.6 times the nominal wall thickness at their base to avoid sink.
  • To maintain uniform wall thickness, bosses should be cored to the bottom of the boss.



Plastic threads used for joining parts can be machined or molded-in

  • When designing molded-in threads, avoid feathered edges and include radiused roots in order to minimize stress concentrations and to keep the walls uniform.
  • Sharp edges can be stress concentrators in plastic parts. Thread designs should consider this.


Draft Angle

  • Design parts with a minimum of ½˚ per side draft in order to accommodate easier ejection from the mold.


Amorphous Versus Semi-Crystalline Materials:

In amorphous materials, molecules are randomly oriented and intertwined. Polymer molecules have no ordered structure. These materials have no identifiable “melting point” but progressively soften through a broad temperature range. Unfilled amorphous materials are typically isotropic, shrinking equally in the flow and transverse directions. Even fiber-filled amorphous materials typically have low shrink and good dimensional control.

How to Choose a Reliable Plastic Mold Factory

How to find a reliable plastic mold factory? It has already become a pain in the neck for us to find a specialized mold maker that offers a reasonable and yet affordable price. Many are concerned that the quality of the product does not meet their requirements or the delivery is not punctual. With so many mold makers active on the Internet, it is not known which are the most legitimate, and most suitable for them.

plastic mold factory in China

  1. Before selecting a reliable mold processing factory, you should first start from the product you would like to develop, as well as the market positioning of the product. Mold makers are generally divided into many industries, such as medical equipment casings, home appliance molds, and game console casing molds, etc. It is not that the largest and best plastic mold factory is the most suitable for you, nor is that a small mold maker is not worthy of consideration, but you should make a choice according to your own project, thus keeping unnecessary expenses under control.
  2. Investigate whether the mold maker is a one-stop service provider that offers services ranging from mold desigplastic injection mold in chinan and making, to product injection molding and plastic casing surface treatment (spraying and silk screen printing, etc.), so as to avoid multiple suppliers participating in the final production of the product, which not only minimizes risks, but also lowers the cost.
  3. Choose an experienced team. Rich experience in production is also an indispensable factor for a high quality mold factory. Only with rich experience in the production of various kinds of products, can a mold maker solve the diversified problems faced during production.
  4. Quality must be guaranteed, with on-time delivery. To effectively communicate with the cooperating manufacturer, it is necessary to know the mold design rationality of the mold maker, and design changes should be minimized from both your own and the maker’s sides, to improve the mold design and manufacturing process, while guaranteeing great communication between product and mold engineers, thus achieving product quality assurance, as well as JIT (just in time) delivery.
  5. Last but not the least, we must also check the aftersales service capabilities of the plastic mold factory.

Sositar Mould, a joint venture that specializes in the manufacturing of precision molds and plastic products, is a great choice with independent import and export rights, and over 10 years of experience in plastic mold manufacturing. With integrated mold making and injection molding capabilities, Sositar mould boasts a complete set of mold making and plastic injection molding equipment to ensure a reliable quality and JIT delivery!


How to Choose the Right Plated Coating for Improved Mold Performance

Many mold makers and molders have had great success with one particular coating and have used it for all of their applications. Unfortunately, there is not a magical coating out there that works in every situation. Many times, excellent coatings are used in the wrong applications. Speaking from a player’s viewpoint, one of the major challenges is correcting problems caused by another plating company applying the wrong coating for a particular application. When plating is used properly, the positive results can be stunning.

There are many causes of wear and corrosion in plastic molds that can contribute to greatly reducing mold life. Plating can solve many of these situations. However, these coatings also can improve the performance of molds in many other ways. A basic knowledge of plating is necessary to make an educated choice for properly solving your particular problems. There are more than eight different plated coatings for molds. It is the intent of this article to help molders and mold makers take advantage of these benefits.

Types of Plating


Types of Plating

There are two basic types of plating – electrolytic and electroless. Electrolytic plating requires electricity to make the process occur. There is a positive and negative charge. The positive is called the anode and the negative is the cathode. The part to be plated gets the negative charge so it becomes the cathode. The anode is made of conductive metal – such as lead – and becomes the source of the positive charge. Hard chrome plating is one of the oldest electrolytic plating processes. The chromic acid solution is the medium by which the current transfers. When the plating process occurs, the negative and positive ions transfer in the solution causing a metal (chrome) to reduce the base metal of the part being plated. A good analogy would be to look at it as the reverse of EDM. Because the process uses electricity, the plater is constantly fighting against the laws of nature.

The old rule still holds true: electricity travels in straight lines and goes to the closest point. On sharp corners, there will be a heavy buildup of plating. In the recesses, the plating will tend to be thinner.

Electroless plating, such as electroless nickel, is just the opposite of electrolytic plating. Additives in the solution take the place of electricity. These additives are known as reducing agents. Since all metals have a charge, when the reducing agents detect the base metal charge in the plating bath, they start to react. This causes the metal in the bath solution – in this case, nickel – to reduce the base material of the part being plated. No electrical current is required. Wherever the plating solution touches the base material, the plating will adhere. This gives the plated part a very uniform deposit and the plating thickness can be controlled within .00005-.0001, even on complex shapes.

Within these two families, you have several types of deposits. These different types include composite and alloy deposits. As a generality, if you need a perfectly uniform deposit in a complex shape, electroless nickel deposits are best. However, hard chromium is the hardest deposit and has an excellent release.

How to Choose

When choosing to plate for your mold or mold components, you must first identify the problem to be solved or the problem to be prevented. The first question you should ask is “What is the cause of this problem? Is this problem the result of corrosion or wear?” If the component has previously been plated, this may be difficult to determine. Have your plating vendor look at the component to determine if it has been plated and if so, what type of plating was used.

Abrasive wear can occur on compression molds that use mineral or glass-filled materials. These materials can cause a scouring action on the mold surface. In transfer and injection molding of thermosetting materials, wear often is detected in the high flow areas such as in the sprues, runners, gates, and portions of the cavities and cores that are directly opposite the gates. In injection molds for thermoplastics, wear most commonly appears on the surface opposite the gate.

Most damage results from continuing to run the mold after flashing occurs. However, there are other sources of damage of which to be wary. These sources can include water contacting unplated surfaces, causing corrosion; water condensing in the molds; seepage through porous metals; and leaky pipe fittings and “O” rings. Where chillers are used for mold temperature control, condensation of moisture on the mold surfaces can sometimes occur even while they are in full operation. Careless handling of hoses and feed lines during hookup can leave water on the mold surface. Corrosion is progressive and even if the molds are stored after being sprayed with an antioxidant, a few drops of water or condensation can cause tremendous and costly damage.

Another source of damage attacks from acids. These acids may form after exposure to corrosive materials generated by thermoplastics decomposition (often due to overheating). Overheating can occur in the plasticizing cylinder, the hot runner system or in the mold cavities as the result of two small gates, or inadequate venting or cooling systems. During the molding of PVC, a small amount of hydrochloric acid is formed, which is extremely corrosive to the mold cavity.

Electroless nickel, by its very nature, is an excellent corrosion barrier for most mineral acids, whereas these acids will attack chrome. Stainless steels also can be susceptible to attack by chlorine or fluorine containing plastic, leading to pitting or stress corrosion cracking. This can be eliminated with a high phosphorous electroless nickel deposit over the stainless steel.

With so many different types of molding and even more types of materials available, there is no easy answer as to which coating will best enhance performance. An investigation into these coatings is worthwhile because if your molding operation is left unprotected, it can create corrosion, erosion, materials flow or release problem. The proper plating can make all the difference. Before you make that critical decision, call your plating vendor of choice and ask which coating will work best for your application.

sositarmold How To

How to Make Your Mold Shop Stronger

In March of 2001 the U.S. economy slid into a recession. By the time the powers that be decided to make the announcement in 2002 it was old news. Many organizations, including those in the moldmaking sector, had already taken a hard hit from the economic downturn, and were taking measures to survive long before it was made formal. It’s now almost 2004 and they are still in a survival mode.  There’s no need to announce that the economy is taking longer to recover than anticipated.

Today’s companies are facing issues and problems exacerbated by the economic downturn.

Downsizing, reorganization, restructuring, cost cuts, hiring freezes and other measures have been taken to stay in business in a tough economy. Managerial calls to employees to embrace change have sometimes been met with resistance and uncertainty. Low employee morale is prevalent. Although overall competition has always been tough, today competition from foreign outsourcing is fierce.   These are just some of many overwhelming challenges organizations must face. Most companies are trying to figure out what to do until things turn around. But who knows the shape of things to come or the duration of the change?
Although each company has its own issues and challenges, here’s what you can do now to help drive business growth:

Accept that times have changed and what has worked in the past may not work in the future. We must use change to provide the creative tension to keep us moving forward. Think of tough times as opportunities to tap into your creativity; get your organization running like a well-oiled machine and seek new ways of doing business.

Rethink your entire business strategy. Ask these questions:
Have we been complacent for too long?
Where might there be opportunities to expand our services?
What more can we offer?
How can we penetrate new markets?
How can we do more with less?

Take Advantage of Foreign Competition

Business is looking very interesting on an international basis for companies in the U.S., especially in certain emerging markets like Russia and specific markets in Latin America such as Brazil.  Also, the Chinese market continues to do quite well despite the fact that their currency is overvalued.

Speed and execution are the keys to taking advantage of these markets.  Companies in the moldmaking sector that respond to these emerging situations will be the most competitive. This will be especially true if growth accelerates and companies find themselves with inadequate capacity to meet demand. Smart companies are moving forward aggressively in terms of new markets, emerging growth sectors and product opportunities through strategic alliances on an international basis.

You must be receptive to seeking out innovative new products that will enhance your current product line and stimulate business growth.  Learn what new products and technology are available that can help to expand your business. You need to accept that finding products overseas can enhance your current product or add to your product line. Thoroughly explore the alternatives. Some companies have found critical new products and technologies from outside companies. If you are not receptive and highly conscious to outside new technology and overseas markets, you may quickly find yourself acting in a defensive position simply to survive.

Invest in New Technologies

Invest in technology that reduces your operational cost, improves quality and increases your contact with the customer. Pay attention to customer-relationship management regardless of the size of your company.  There are new technologies being created everyday, use this as the driver and the tool for business growth.

Maximize Your Business Strategies

Make this economic downturn a good time to re-examine your core business values. It helps to seek input from your employees by involving them on a day-to-day basis. Asking them for their extra effort allows you to crosstrain people in various positions. Make sure they know that they play a strong role in developing the company’s reputation and establishing customer loyalty. When things do turn around, you will have a competitive edge because your employees will be more supportive and understand the big picture to a greater degree.

Going back to basics means working harder than ever to sustain and develop strong business relationships. Talk with your customers about where they see their business in the future and identify how you can assist them in selling more of their products. No matter how often you’ve heard about the importance of customer service, it always warrants reinforcement. If you want to obtain customer loyalty and remain competitive, your level of service must far surpass your competition. If what you sell or offer is essentially the same as other competitors, differentiate your approach to marketing and sales. Be willing to take a risk. Tap into your creativity and think about what you can do to stand out in the minds of your customers. Innovation will make you sharper, better and bolder by definition.  By giving them the help that they need, you will create quality customer relationships that mean long-term profitability.

Companies that institute smart strategies and believe in their employees, products and services are able to introduce new products and differentiate themselves from their competitors by portraying a higher level of service in every aspect of the customer experience. This can gain a competitive edge until things turn around. But keep in mind, that when they do, business will be very different. Determine your future and its potential.