Adding Texture to an Injection Mold

I was asked to add texture to an injection mold. I've never done this before, but heard that you can use sand blasting. I first tried an air eraser, which didn't work well. Then a full-sized sand blasting cabinet, which did work.
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00:00 Open
01:08 Intro, CAD, and CAM
03:48 Milling the mold
05:51 Masking the mold
08:27 Sandblasting
09:02 Removing the tape
10:52 Re-machining the bosses
11:29 Injection Molding
17:34 Wrapup

[@jackorlove4055]

At my shop we do plastic injection mold making, and what we use to tape off areas is this general purpose yellow vinyl tape. It offers smooth adhesion, but isn't a mess like duct tape, but also withstands the force of sand blasting. It comes off like butter if you use kerosene. In fact, most adhesive messes are almost completely destroyed by kerosene, so it might be worth keeping a bottle around. Spray it down with kerosene, peel off the tape, lightly clean up with tissue or a very clean, soft rag, and then spray down again, then spray it down with methanol. Clean as ever. The nice thing about the yellow vinyl tape as well is it can be CUT and SHAPED very neatly with a sharp knife, so you can maintain a sharp line on your part. Hope this helps!

[@lxc3909]

I have several years experience with media blasting (from two former jobs and as a hobbyist). Re-machining the vertical faces is an interesting approach; however, this could have been done without re-machining, too. Those vertical surfaces could have been masked several different ways. Masking tape is effective for most media blasting (without the aggressive adhesion of duct tape)--so long as the blasting process does not dwell on one spot too long. Those vertical faces could have been masked with masking tape. Alternatively, there are masking liquids that can be brushed on and left to dry. Even "rubber cement" could be brushed on as a liquid mask. Some paints, including fingernail polish, can work, too; but you have to be aware of the ease (or difficulty) of removal of a brushed on mask. Experimentation, with scrap pieces is important.

[@JohnSL]

I did think about trying to mask the walls. But it was very quick to put the mold back into the machine to mill these walls. If I hadn't had leftover tape on the bottom of the mold, it would have come out perfectly. I'm not sure I'd get as precise results with masking those vertical walls.

[@PeckhamHall]

If you can't use ejector pins, use inserts for the cores, get a slide hammer to connect, and ask your a material supplier to get you a bag of lubricant for p.p, p.p normal has 0.2% but you can add more to help, it's like a opaque jelly wax.

[@cncrouterinfo]

I have been wondering how this works for years! Thank you for showing how it works.

[@RyanRife]

I was just thinking about how this was done…also curious about that faux leather look.

[@IrisPPG]

I extract cast urethane parts using an air gun. Since you have holes that go all the way through it would be super easy to use the air pressure to pry them out from the bottom up. Just use a rubber tip.

[@sayeager5559]

I carry that same razor knife at work. A medical scalpel with a fresh blade makes cutting that tape very easy. I always wipe down with acetone after removing tape.

[@DragonflyEngineering]

Thanks for the Dragonfly Plug John. Nice looking part! I want to get into molding thick parts at some point .

[@drubradley8821]

Silicone Carbide media is what we used for textured surface requirements, which can be had in many grit sizes. With time and allot of plotting and keeping of test samples, we could plan out with which grit size of the carbide media, at what PSI, all pending which material alloy was being used to predict a particular surface finish. It was a crazy catalog process, but, all in all, I think what your results were, came out really good. Too much texture or deep patterned texture, pending the draft angle and make pulling a part out exceptionally difficult if not impossible. Even with a good enough draft on the walls, and core pins or "knock-out-pins" the drafted walls with heavy or deep texture, will start to wear the texture out on the cavity. Granted, that is determined by quantity or the run, the material being injected, the draft angle, the depth of the texture and how cool the finished part is and a few other parameters, of course, no concern for what you are doing, and just adding my 2 cents, beings you asked. There is another factor, virgin media provides one type of cutting action in surface finish, where as, recycled back into the sand blasting cabinet type system, the second use, on out to 50 times used media, (no matter the type of media being used, some less then others) that used media will cut completely different. Often times, sand blasting media on the second to fifth use or pass-thru, will actually cut much better, as each grain gets broken or fractured. The next time around, the brand new edge of the grains cuts better. Please note, some sand blasting media burnishes, polishes, work hardens, cuts, and a few other actions that are more specialized. Just in case you all didn't know. It is important to know, regular beach sand is something that you NEVER want to use as breathing any of that in, can cause serious respiratory issues that can lead to death, not much different than that of mesothelioma, called silicosis. Bad way to go out. I enjoyed watching this process the past few videos. It is important to note, anything I have mentioned, is in no way meant to insult you or anybody that may read my comment. I do not claim to know it all. I am always willing to hear of methods or clever ideas that I have never learned. I am open to be asked questions and I will assist in answering to the best of my ability in the greatest of detail that time permits.

[@JohnSL]

Thank you for the detailed reply. It gives me some very useful information for more research. Given how small my parts are, I should be able to use one of the small portable sand blasters that would not recycle the media. From your reply, it sounds like that would actually produce more consistent results.

[@dawidwasielewski8669]

Hey Bradley, my name is David and I'm from Poland, I have some questions, if you have time to answer them, please let me know how I can contact you. Thank you in advance

[@drubradley8821]

@@dawidwasielewski8669 Sure, what is your question(s), I will do my best to answer them. If I do not know the answer(s), I bet that we together, including the channel owner "JohnSL" can come up with something for an answer or direction, at which point, we all get to learn something together, and we'll all be better for this effort of researching the unknown's.

[@dawidwasielewski8669]

@@drubradley8821 Thank you for your answer. I have a small injection mold service in Poland. To be completely happy, I lack the knowledge of how to make a VDI texture using sandblasting or acid, and unfortunately in Poland it is a closely guarded secret. There are only 2 companies that do this and they have a monopoly on it. I'm a toolmaker, so I know a bit about this profession, but I've never dealt with textures, and we often get tools with a damaged texture (mainly VDI after EDM). I heard that a mixture of corundum and glass beads is used for this, but I do not know the proportions, nor the thickness of the sand, nor the angle, nor the pressure. Can anyone give me the exact instructions? The rest will be in my hands, I will try.

[@dawidwasielewski8669]

@@drubradley8821 anyone?..

[@AlmostMachining]

very nice John!!!

[@petergamache5368]

Duct tape is "good enough" for many jobs but seldom ideal. The best sandblast mask I've encountered is called Oramask - it's a self-adhesive vinyl product you can find at sign supply stores. You can apply it to the mold while it's still in the vise and let the CNC trim it for a perfect fit.

[@JohnSL]

Oh, that's cool! Trimming it in the CNC would be much nicer. I'll have to try that out. Thanks.

[@erikcederb]

I second this, Oramask (no. 831 IIRC) is the way to go

[@PeckhamHall]

Polypropylene likes the stick to polished surfaces more than textured surfaces in most cases depending on finish.

[@SwissplWatches]

great video. thank you

[@jbrownson]

Thanks for the video, always learn something

[@roylucas1027]

Interesting video. I’ve been burned by the glue on masking tape before. Frustration.

[@josdrolkoppers1030]

Great video! I made some small molds myself and instead of using the tape, you can add 1mm to the mold thickness, sandblast the whole surface and mill the finishing 1mm to have the smooth closing surface. Keep up the good work!

[@JohnSL]

I thought about doing that, but I don't remember why I didn't do it that way.

[@michaellowry1888]

Great video! I think aluminum oxide or some other like 80 or 24 grit or ground glass can be really coarse for large texture

[@subuser9627]

People who work with stainless steel know a lot about sandblasting, because you usually don't paint it. And about the tape, maybe it is useful to clean your work with acetone.

[@jadoncramer6512]

WD-40 takes of the adhesive really well

[@JohnSL]

I used WD-40. But, clearly I didn't do a good enough job.

[@user-xk4wn1vj8l]

Can you apply 2 textures in the same mould without putting a departing line, meaning a smooth transition from one texture to the other?

[@RyanRife]

Wonder if oramask would work better than duct tape. I know with wood cnc’ing I mill through the oramask and wood without any issues and it leaves a flawless cut out in the mask.

[@TheMasterElite]

John, this channel is fantastic and I've learned a ton from it in the short couple of months I've been aware of its existence. I am curious what all is involved for procuring both a good mill for aluminum molds, overall tooling costs [I don't imagine aluminum is very expensive but I've heard replacing bits can get expensive for precise and detailed mold work], and what you could suggest in terms of good resources for learning some of the art of moldmaking. I am experienced in SLA/FDM 3D printing and am currently exploring using some high-temp casting resin with SLA process to make some short run molds, but I understand they don't last more than 20-50 cycles, depending on detail, size, quality, etc., and for moving beyond prototyping I am going to have to use some sort of injection molding process and that has sent me on this marvelous journey. Also, what do you think of the Buster Beagle 3 compared to the older model?

[@JohnSL]

I used to use a Taig CNC mill to make molds, so that's a good choice as a starting point. If you get one of their ballscrew versions, they're plenty accurate enough. I believe the prices of their CNC machines is in the $2K-3K range. Tooling isn't that bad for aluminum. As long as you use the right feeds and speeds, they last for a long time. This video of mine should help with that: kzbin.info/www/bejne/bHnTeamrrq91fJY As to the BB machines, I don't know a lot about them.

[@peterjensen6233]

Harbor freight sells a hand held bead blaster, yes I know. $22.00. It’s perfect for this texture job. You can easily use different grits as needed.

[@JohnSL]

Thanks. I was thinking about getting one of those, now that I know what works.

[@GregsGarage]

This was a great look into the various things that can affect a mold and the machining. The tape residue was a surprise! It looks like you are using a straight endmill to machine the walls. Have you ever used a tapered mill to do that so you can eliminate the time it takes for the step overs? I've used tapered mills in wood, but haven't ever used them in my mill on aluminum.

[@JohnSL]

I know there are end mills with different tapers, and I believe that's what they used to add draft before CNC machines. With a CNC machine, it doesn't take very long to program the tool paths and I can have the draft be any angle I want. And it means I don't have to use a specialty end mill that would take up another slot in my tool changer.

[@GregsGarage]

@@JohnSL I guess I'm thinking about large machining projects that are kicking out 1000's of parts... I need to think about molds as relatively small parts that are one-off situations... In that case, 10 minutes of surfacing passes is just a drop in the bucket.

[@GeorgeGraves]

I'd love to know how they do those more complex organic like textures.

[@JohnSL]

My understanding is that these involve chemical etching.

[@leonwagner2687]

I think it's better to use a plotter and cut the foils from the template

[@David_11111]

yay

[@billstrahan4791]

Great video as always! I’m curious if it would have been possible to leave several thousandths of surface on the mold halves so they could be faced to final dimension after blasting, thus avoiding the tape altogether! I have a part I need to produce that will involve some texture so I’ll need to figure that out for certain, but that was my planned approach. I figured as long as I had a reference to probe that didn’t get affected by texturing I could just do my final facing passes afterwards.

[@JohnSL]

I did think about doing that, and I believe it would work well. In this case I wanted to test the mold and adjust it before adding the texture It didn't take that long to mask the mold, and I now know I don't need to mask the bottom.

[@rexmundi8154]

Nice work. I was concerned about the end mill marring the sand blasted finish on your cleanup pass. Even if it was registered perfectly, expansion caused by different temperatures, bounce back of material, or of a bunch of other factors can cause a obvious mark when re-milling a part. I never considered injection molding as a process I could do, but I need a very small hydraulic coupling with a weak check valve that is made of PEEK plastic. After seeing your work, I’m wondering if I could injection mold something with a ball and spring encapsulated. I’m a machinist running the machine shop for a company that does science experiment development for the International Space Station

[@JohnSL]

I've found that keeping the end mill 0.001" above the floor is enough to keep from marring the finish. Unless, like in this case, something gets under the mold so it's not flat against the parallels. In other words, it was operator error in this case.

[@machineman6498]

👍

[@broganmcintyre8594]

Where can I get an aluminum mold like this made for cheap?

[@EvanZalys]

Very nice! I'm curious -- why are you using this press instead of the morgan press? Also, who makes this press?

[@JohnSL]

Thanks. This mold is meant for a Travin TP-1, which is a smaller machine than the Morgan. More importantly, the customer specifically wanted a mold made for a TP-1.

[@stefandebruijn3167]

Just wondering... can't you just superglue some siliconcarbide or fine sand? With superglue I mean the heat resistant (250C) superglue variants; just add a nice squirt, let the excess flow out so you end up with a very thin layer, and throw in the sand. That process would be much faster if it works.

[@PaulSteMarie]

What's the coolant you're using? Looks almost like straight water, but I'm sure it isn't.

[@JohnSL]

The coolant is Blaser Synergy 735. I like it because it's clear.

[@LtJerryRigg]

Awesome video, fantastic results. I have a small part that I would like to produce via injection mold, are you open to commissions, or know someone who might be? Thank you!

[@JohnSL]

I do. I'm pretty backed up at the moment because of the watch project, so probably couldn't get to it until a couple of months from now.

[@monouvichet7589]

Hello dear I’m interested your video, do you have service mould ?

[@jozefdzugan1828]

Poor position of gate causing jetting effect.. design next against some wall.. surface of plastic is always a little less deep than on tool.. so if you want VDI27 on plastic use VDI30 in tool.. last thing I would recommend is to add any ejectors or at least loose insert of middle bosses..

[@JohnSL]

Thanks for the tip. I could easily have done that in this mold. As to ejector pins, that would have made the mold more expensive. For these desktop machines, keeping the cost of the mold down is important. Plus, many of the desktop machines are such that you have to remove the mold from the machine anyway. I've talked to other companies that make small run parts with desktop machines and found they do pretty much the same thing. No ejector pins, and then pry the part out of the mold.

[@jozefdzugan1828]

@@JohnSL OK I understand that ejector pins are not suitable for this kind of job but anyway try to consider using separate inserts for inner shape so you can disassemble them from top side firstly with hammer and some pin without touching plastic part (plastic part sticks mainly on inner surfaces due to shrinkage) and rest will go easily from outside surfaces so you can be sure that plastic will not be damaged... BTW overall it is great job and I like your content of the channel 👍 keep going forward.. if you will have some more complicated jobs or anything not sure about let me know I can help you 😉

[@jwilham]

i only watched like 18 secconds of the video but this seems like a waist of time.