How To Reduce Injection Mold Polishing Costs

Now, wouldn’t that be great if you knew how to reduce your injection mold polishing costs? Mold polishing is a major bottleneck in the plastic injection mold making process, so here are some tips and methods that might help to lower the mold making costs.

Assuming that a shop has a decent volume of work to be polished, there are really only 3 options available for getting the job done right and in a timely manner.

Injection Mold Polishing
Mold Polishing Stones

Isn’t it ironic that the injection mold making process is highly technical but, in the end, depends on hand finishing ?

Three methods of polishing injection molds

  1. Send the work to a dedicated, professional polisher.
  2. Use skilled moldmakers to do the polishing.
  3. Train an in-house mold polisher who handles the vast majority of the work.

Using a professional service

This is a great option for many shops. There are several benefits to sending your work outside:

  • It is very often much less expensive than using your injection mold making staff or in-house polisher.
  • The turnaround time can be extremely quick and makes scheduling easier, sometimes.
  • The quality is usually more consistent, especially once you develop a relationship with the company.
  • Using an outside company eliminates the expense of hiring another worker and paying the wages and benefits associated.

Drawbacks of outsourcing mold polishing

  • Shipping and scheduling can be nearly impossible to fit in with the hectic nature of moldmaking. The work flow rarely proceeds as planned, making it difficult to send the workpieces out for the necessary days.
  • Communication can be exceedingly difficult when it concerns things like shut-off areas, surface finish requirements, areas to avoid, polishing areas that will subsequently be machined away, etc.
  • Some finishes do not require that much skill and the expense of an outside company cannot be justified. It might just be easier to do it in-house if the job is simple and relatively quick.
Injection Mold Polishing
Mold Polishing A Helmet

Communication is extremely important, both for polishing in-house and outsourcing. Don’t assume anything.

Using skilled moldmakers to do the polishing

This method is probably the most common in small shops, or those that do not require highly polished molding surfaces. Some of the benefits of this approach include:

  • This approach makes it much easier to maintain control over the job. The mold can be polished at various intervals in the process and the moldmaker understands what needs to be finished and what can be left alone.
  • The moldmaker requires little instruction and this can be done face-to-face, rather than over the phone or in emails.
  • Usually¬†the quality of work is excellent due to the skill level of the moldmaker and the pride of craftsmanship.

Cons of using moldmakers to polish injection molds

Like a lot of things, your strength can become your weakness, and this holds true for this approach.

  • The high level of skill possessed by the moldmaker enables him to do a good job polishing, but it also takes him away from other tasks that are likely more difficult to outsource.
  • Quality can be spotty, due to the fact that polishing is just not for everyone. The man might be great at mold assembly or EDM, but just does not possess the ability to adequately polish a mold.
  • This approach can get expensive very quickly. A skilled moldmaker demands a relatively high wage, and because mold polishing is more of a side-line skill, the hours can start to add up very fast.
  • It is just the nature of mold polishing to be tedious, there is no way around it. Some individuals are fine with the boring nature of this work, but others quickly become bored and thus become discouraged or inattentive.

Using an in-house mold polisher

For companies with a decent flow of work, this is the optimum choice. As long as you have more than enough work to keep a man or woman busy polishing, this is the best choice for most shops. Here are some reasons to use an in-house mold polisher:

  • If you can find or train someone to do quality work and they enjoy it, you have accomplished a real feat. The moldmakers will no longer be required to do something they possibly dislike.
  • Quality should improve with a permanent or part-time employee. Because this person is dedicated to one task: mold polishing, they will become very good at it. They will not be asked to do other tasks at the same time, such as running EDM’s, CNC milling machines, automatic surface grinders, or WEDM’s.
  • Project management and scheduling become easier. Now that the work is always in the building it can be moved from process to process with the polishing fitting in as needed or when the workpiece is available.


All in all, mold polishing is often an overlooked aspect of moldmaking. However, it is the final finish that people see and though the part might be dimensionally correct and the molding cycle times faster than quoted, if it looks bad, it is bad.

Careful analysis of the workflow, type of surface finish required, space requirements for a mold polisher and quantity of work are some considerations that must be taken into account when deciding to take on an in-house polisher.

One comment

  1. Why not call a mold polishing company that comes to your facility to do job in house finish gets payed and then leaves and will be on call if needed

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