Turnkey solution to control plastic injection molding tolerance

There are lots of people are talking about that how to control the tolerance for plastic molding. I combine my experience with a few exporter who have more than 20 years experience for molding industry. I hope following information will be very useful for you.

What will affect the plastic injection molding tolerance

  • Plastic injection molding resin
  • Mold manufacturing & injection molding project management including engineers, sales & communication etc.
  • Plastic injection mold machining accurate
  • Mold design concept
  • Molding parameter
  • Injection molding machine quality including brand, local or import one
  • Injection molding machine selection including machine size, screw diameter, injection volume and clamping force etc.
  • Quality control including inspection of mold components, electrode and plastic products

First of all we talk about the mold manufacturing & injection molding project management

Lots of people miss to control this on the plastic product tolerance. This is first process we should control the tolerance. We should control from the samples if you are mold factory, if you are mold or plastic product buyer, you should control this on the information offer process.

What we should offer to mold manufacturing factory and molding factory or ask from buyer to control the tolerance?

Plastic product 2D drawing: There should be tolerance label for all of the dimensions. This is target what customer need to reach. If you have surface finishing and secondary process for this products, please offer this information on the 2D drawing. Also please throw away the habit to talk to your mold manufacturing supplier for this kind of requirement on email. If not, you have risky to have your supplier to miss information if the one you are working have no good project management.

Plastic product 3D drawing : Have this drawing to provide to your plastic mold maker, then they check the details of the plastic product on the drawing. Also if your good and professional mold supplier limited on the capability, they will reply you.

I suggest you to read plastic injection mold life on our blog to know more about that the mold life for the tolerance and cost. Normally the accurate mold should be made with through hardness core and cavity. Please offer mold life for mold manufacturer.

Above process is to control the plastic product tolerance during the quotation, this is the communication process, and is the basic process to have tolerance under control.

How SEASKYTOOLING to control the tolerance on the quotation process?

  • Lessons for all of the salesman to understand what we should ask from customer
  • what we should ask based on different customers
  • We clean individual cases up during our service, use this to help you and our salesman
  • We have easy understanding form to collect customer demand to our CRM
  • Professional engineers coordinate with salesman to check and study the information from you
  • Also most of salesman have mold engineer experience

Based on above, we make sure we can get the enough information from you to proceed the quotation and assure you have no risky to miss the tolerance control.

Control the tolerance on different plastic resin

This is one of most important process to control the tolerance.  Different resin on injection molding with different dimension even if it is the same injection mold due to different resin with different shrinkage.

For the POM, PP and PE etc resin, they have big shrinkage, it is more difficult to control tolerance than PC, ABS, Nylon with glass fiber and PC/ABS etc. Normally PC, ABS and ASA etc. plastic resin with shrinkage lower than 6 ‰ is easier to control a few dimensions with +/-0.02 mm, assure it is possible to control to more accurate tolerance for a few dimension. We do not suggest to use the high shrinkage resin to have accurate plastic parts.

Control the tolerance on plastic mold design process

This is one of whole process to check the information provide by customer and manufacture the information on plastic mold design and input on plastic mold factory for mold manufacturing. Your mold supplier should consider following for the mold design and even more than these:

  • Plastic resin shrinkage
  • Plastic product gate location
  • Safe steel for accurate dimensions
  • Use the inserts as possible for the accurate dimensions
  • Use the inserts as possible for the easy breaking feature of mold
  • Consider the suitable injection molding machine
  • Learn the plastic resin specification and input this on the mold design
  • Consider the molding parameter during the mold design
  • Prepare the solution to prevent the deform, short shot, burning etc. common issue during injection molding
  • Mold designer have full check list to check the mold design even if you think you are very  professional
  • Run the mold flow to test the mold design and plastic product design
  • Optimize the mold design and plastic product design

Control the tolerance on plastic mold manufacturing process

  • Choose the right process to manufacture plastic mold components
  • Inspect plastic mold components including the electrodes and mold inserts
  • Assure the plastic mold components is accurate
  • Relieve the stress for the large mold core, cavity or mold plates after manufacturing
  • Measure the plastic mold components and record
  • Inspect plastic products dimensions after injection molding trial and record
  • Measure deviated dimensions on the mold after mold trial. Find the clue to improve the dimensions on the mold
  • Choose the right injection machine according to your injection mold including choose the right screw of injection machine based on the resin and plastic part, clamping force, injection volume, Min-Max mould thickness and ejector stroke etc.
  • Record the molding parameter during mold trial, not only the parameter on the injection machine. You should also record the mold temperature, test the actual temperature of mold and set up temperature of injection machine.

Plastic injection molding tolerance control

If the mold is released for mass production, you should also control the tolerance of the injection molding parts. First of all you have to control the whole dimension, at least you should measure the biggest length,width and height of product. If this have no big change, this means your injection parameter should be correct probably.

Give more importance on the first 100 shots once you start the production. Once the mold running a few hours, the parameter should be not the same, you should check the tolerance, this is the reason why we suggest to check large size and accurate dimensions each hour. Please noted the mold trial is different as the production. Even if you got a good shot on mold trail, it is not the case you can get a good shot on long time production. Please check and record, you will learn lots of information.

Also you should measure the accurate dimension at least per hour to make sure it is correct. You can measure it more frequent based on your production quality control.

You should also check the following things during injection molding

  • Plastic injection molding parts color
  • Plastic injection molding parts surface finishing
  • Plastic injection molding parts small feature including ultrasonic welding line, small bosses, small posts and small ribs etc.

About Hedy Yeh

Major in machinery and tooling in university from 2001 to 2004; Worked for plastic mold design, mold manufacturing and mold and production project management from 2003 to 2008; Working for mold marketing and mold project management from 2008 till now My facebook page