Molding Custom Plastic Parts - What you need to know

Custom plastic molding is often perceived as daunting and it can be if you don’t have the right guidance or information. The great news is that, in this article, we enlist every detail that you need to know about custom injection molding services so that you can ask the right questions to get the right information from your tooling supplier and injection molder. 

It’s imperative to note that manufacturing durable plastic parts through custom plastic molding requires both a plan and a design. A quality manufacturer will generally have design engineers that can create the perfect custom parts by utilizing their experience in designing an injection mold.

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Design Guidelines Checklist for Custom Plastic Molding

You should note that there are certain guidelines that one should know about to ensure that your custom plastic parts are manufacturable and deliver the required quality. We have shared a checklist of such parameters. These are enlisted below: 

plastic molding design checklist
  1. Part Job Specifications: In order to get the best possible design for your product, it is imperative to specify every aspect. These aspects include tensile requirements, dimensions, elemental factors, pressure and chemical exposure.   
  2. Material Selection: It is important to understand the extent of application before choosing a material for the product. This helps to produce parts that are not only functionally operative but also durable enough to withstand its environmental conditions. If you are unsure, ask your injection molder for recommendations.
  3. Maintain a Uniform Wall Thickness: One of the most important factors to ensure smooth and successful manufacturing is maintaining a uniform wall thickness so that there are no weakened spots.
  4. Rib Design: Another factor that contributes to stability of the part is rib design. Rib design increases stiffness and durability in the plastic part without increasing the thickness of the wall.  
  5. Design Elements: In order to ensure that the product is further durable and can withstand endurance, various design elements such as bosses, weld lines, vent placements and gate placements should be considered. 

Should you invest in getting a custom prototype?

The general notion is that prototype tooling is unnecessary. It is often regarded as an extra step that simply increases costs. In our experience, it can be quite the contrary especially if it involves producing complex parts, parts for high production volume, new ideas verification or if you require parts, quickly for verification

When custom injection molding services are carried on without a prototype tool, it typically leads to more adjustments and potential problems. Generally, a series of adjustments may be required which can turn out to be both costly and disruptive. 

Prototype tooling can generally vary between 20-50% of overall production cost depending upon the complexity. We understand that the investment is significant, but saving on prototype tooling may turn out to be costlier in some cases. 

You should also note that prototype molds are often built with softer steels or sometimes, even with aluminum and usually do not last very long. Their lasting capacity is dependent upon various aspects. Prototype molds may last from 1000 shots to 50,000 shots, depending upon the part, plastic material and steel material.

custom plastic parts

Where can you find Custom Plastic Injection Molders?

  • Google – Google is one of the best sources that can provide you with custom plastic injection molders in your domestic location. 
  • Thomasnet – Thomasnet connects buyers and suppliers within the industry. You can get an insight into various suppliers on Thomasnet. In addition to being a great database, it can also help you to search for supplier with categories, certificates, location, niche and industry 
  • Plastic News Directory – You can browse businesses at Plastics News Directory to find custom plastic injection molders. 
  • Trade Shows such as MD&M, TAGMA – Trade Shows such as MD&M, TAGMA are a great resource for meeting with custom plastic molding companies. You can speak with the representatives and understand their company better. You can also take a look at their work samples, that they often bring to their booths and understand the quality.

Top Qualities to Look for in a Custom Plastic Injection Molding Manufacturer

A custom injection molding services company that you choose to work with should be like an extension of your team but how do you choose one? What are the qualities to look for in a custom plastic injection molding manufacturer?

Well, now that you know which questions to ask for? We assure you that selecting a custom plastic molding manufacturer won’t be tricky or daunting. Furthermore, here are some basic inquiries that you must make with your custom mold manufacturer to ensure that you are making the right choice: 

Open and Clear Communication

One of the first and primary qualities to look for is their ability to communicate effectively and transparently with your team. 

You can ask them the process of placing an order and judge upon the following to understand if the custom injection molding services company is reliable or not. 

  • Understand if the series of events are detailed enough or if they are simply an overview.  
  • Are they open enough to receive feedback upon the design or does it stop right, after the first round of drafts? 
  • Are they willing to send you prototype samples? 
  • Do you have a way to contact and connect with the engineer/manufacturer to communicate? 
  • Is your manufacturer willing to make themselves available to include you in the development of the product?
  • Are they willing to update you upon the progress of the project/mold making at regular intervals. 

In-house Mold Making Services

The next aspect to look for is to understand whether they have their own in-house mold making services.

mold designer

Having an in-house making service helps to manufacture optimum quality molds. This also ensures better lead time for your project and it also helps the manufacturer to incorporate any type of modification that the mold may require.

At VEM Tooling, we build molds in our factory units due to which we have complete control over quality. We either follow customer standards that are set by your team or use our VEM standard design to design and build the mold.

Additionally, we also adhere to using only imported and certified steel to build molds thereby, not compromising on the quality front by cutting costs.


Another important aspect to check for is if your custom plastic manufacturer has the required certifications. Certifications ensure that they are adhering to the standard regulations and are often an indicator that the products manufactured will be consistently of high quality . The factory that you plan to partner with should have atleast ISO 9001 certification.

Mold Making Experience

Experience in this industry is of the utmost importance. While there are various factors that can affect the ability of your manufacturer to build molds and deliver durable products, experience provides surety that the customers trust them, and they have delivered great, durable products in the past. You must inquire about the expertise and the experience of the team.

project planning injection molding

In addition, you should inquire if the mold design team has sufficient experience as they need to have experience to deal with difficult and complex parts. 

VEM Tooling has been building molds and providing custom injection molding services for over 18 years, and it encompasses a team of engineers and designers that have immense experience in producing custom plastic parts that are durable. In addition, VEM Tooling has many employees that work here for over a decade. 

Custom Plastic Injection Molding Process

Any plastic injection molding process includes 3 components –  plastic resins, an injection molding machine, and a mold. The plastic resins are first melted in the injection unit which are then injected into a high quality steel mold. The plastic now cools here, to solidify into the final plastic part. 

injection molding process
running molding machine

A custom injection process that is smooth and seamless should ideally entail the following steps:  

  • The very step by any manufacturer would be to review the injection molding quote. 
  • You shall then be consulted upon various parameters to ensure that all the specifications are met. These include, but are not limited to your project requirements, preferred lead time and budget. 
  • The manufacturing starts only when various details such as materials, components, an approved design etc. are established. 
  • Upon finalizing details about your project, a high-quality injection mold is built. 
  • Once the mold is built, your custom plastic parts manufacturer will send first part samples (T1) for approval to your team. This also generally includes a First Article Inspection Report (FAIR) according to your required dimensions.
  • Once the mold is refined as per suggestions, approved, and the part is within all critical tolerances, your manufacturer begins with your custom plastic parts production. 

Custom plastic injection molding across the globe:

Contact VEM for Custom Injection Molding Queries

VEM Tooling encompasses an extensive experience in custom injection molding techniques. If you have a project in your scope or have questions regarding the development of a complex plastic part, please feel free to reach out to us. We would like to understand the task in hand and provide you with any guidance.