Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Randy Taylor, Advanced Tooling Corporation
Chrome Plating on Plastic Mold
Q. We are suffering a problem with Chrome plating peel-off after 100K shot on plastic molding. How can we improve the set-up or parameter to reduce the stress level in order to have longer molding life.
A. There are as many facets to chrome plating molds and dies. Not easy to sum up in just a few remarks.
"Peeling chrome" This is likely a preparation issue. What is the mold base material, heat treat and hardness? List all preparation steps?. What type of rack and or anode equipment are being used? (lead tank stick style or conforming?)
"Shot life 100", What are you basing shot life on, did you experience more shots in the past or when the bath was new? What type of bath chemistry are you using?
"Longer mold life" means improving the wear resistance of your chrome plating. For this I would need even more information. Let's take care of the first issues you mention.
I look forward to your reply.
Q2. My problem is the peeling off on both cavity and core inserts, instead of mold base. The tool material for these inserts are P20 but a high gloss surface finish is required. So it can reduce the material cost a lots because the mold size is 400 ton.
A2. You seem to describe a typical adhesion problem.
Since the chrome plating is sub-contracted to outside supplier that we do not know exactly the procedures for preparation & plating process. Can you advise clearly the problem on preparation so that we can discuss with our supplier soon.
The tool life or chrome plating life is 100,000 shots. Our experience is that the chrome plating layer is too brittle that will crack easily. Can you suggest any method to reduce the brittleness or hardness on plating layer.
Bad adhesion can be due to poor preparation. Shiny or highly polished surfaces are difficult to chrome plate without the assistance of special cleaning and pre-processing steps such as pumice scrubbing and using a lengthy warm up and reverse etch prior to application of forward current.
Good healthy bath chemistry can affect chrome structure, current distribution and adhesion. Bath and part temperature also affect adhesion.
It is also possible you are experiencing poor adhesion due to highly stressed chrome deposits especially on outboard corners and areas closest to the anode source. These we'll call, "high current density" areas. They tend to plate faster and thicker than other areas and are unstable and susceptible to chipping. To correct this, you will need a well designed part rack, anode and related tooling to apply an efficient low resistance current connection to the part as well as the conforming anode.
Tooling issues in hard chrome plating are complex. In molds and dies, a well designed and built conforming anode is extremely important to chrome hardness, thickness and uniformity. Often plating shops are forced to use only what materials which may be on hand. The end results are often poorly adhered with visual cracking and un-acceptable quality.
Conforming anodes, racks and tooling are critical to a quality chrome deposit. To achieve the best results, these requirements should be reviewed by an expert tooling designer prior to plating. This step can assure that your plating supplier will produce the highest quality chrome product each and every time.
If you decide to take this matter to the next level, you'll have to provide photos and part drawings for review by an expert chrome tooling designer. For this special service, send an inquiry to firstname.lastname@example.org