Page 48 - Plastics News May 2023

How to Select the Right Tool Steel for Mold Cavities

What Are You Molding?

The first thing I take into considera-
tion is the material being molded.
With abrasive, glass-filled materials,
my focus would be on addressing
concerns over wear and erosion un-
less the expected volume is extreme-
ly low. But with the most common
glass-filled materials, cooling is more
critical than with other materials, and
the best steels to address wear have
lower thermal conductivity. Carbide
inserts are the exception; they have
excellent wear properties along with
great thermal conductivity, but the
costs and lead times to replace these
need to be considered.

With corrosive materials such as PVC,
stainless steel is a common choice.
Using cheaper options will require
ith cavity steel or alloy selection ing to accept added maintenance on critical procedures to prevent cor-
Wthere are many variables that the tooling if the payback was faster rosion. On parts that have very high
can dictate the best option. Things cycles or lower tool costs. But price surface-finish expectation, tool steels
that need to be considered are the should never be the main factor. As I that have lens-grade specs should be
material you’ll be molding, cycle-time often say, it’s cheaper but costs more. considered. For molding materials
expectations, part criteria, expected There are pros and cons to each and that do not contain abrasives like glass
volume, tooling costs, and mainte- every option, so it’s important to fibers or corrosive ingredients, P-20
nance. The goal here is not to suggest, know all the angles to understand the steel is the most common choice. But
recommend, or give preference to long-term cost vs. just the up-front with smaller tools for high-volume
any specific steel or alloy, but to offer tooling costs. If you need a steel that production, hardened tool steels are
some guidance you should take into is wear-resistant, you are looking at a always a good option to prolong the
account when making the selection. hardened tool steel. This will increase tool life with reduced maintenance.
I’m not an expert on all the steel types your tooling costs up front, but will On the other hand, aluminum can be
used around the world, so there will reduce your maintenance costs in the an excellent choice for lower-volume
be some not mentioned—I’m only long term. But here’s the twist: Hard- tools to reduce cycle times. But from
writing from my personal experience. ened steels are less thermally conduc- a maintenance viewpoint, aluminum is
Maintenance is the variable I focus on tive, which can impact cooling time not my friend.
most in the steel-selection process. if you don’t put extra focus on the Aluminum & Conductive Alloys
Most tool makers that build, maintain, tool design for cooling. If you go with A few years back there were a lot of
and repair production tooling have a standard tool steel that will not be talk and studies about aluminum and
definite opinions on what they like hardened, your cost will be lower up its positive impacts on mold-build
and don’t like in tool steels. I’ve heard front but your long-term maintenance cost and cycle times, both of which
so many varying viewpoints over the cost will be greater. can be significant. But there is always
years, but I have tried to keep an Price should never be the main factor. a negative that can offs et the positive
open mind by taking the big picture As I often say, it’s cheaper but costs if all aspects are not considered.
into account. So at times I’d be will-
more.
48 PLASTICS NEWS May 2023