Lost PLA First Attempt. Calling all casting experts.

Advert

Lost PLA First Attempt. Calling all casting experts.

Home Forums General Questions Lost PLA First Attempt. Calling all casting experts.

Viewing 14 posts - 1 through 14 (of 14 total)
  • Author
    Posts
  • #24623
    David Cambridge
    Participant
      @davidcambridge45658

      Lost PLA. Calling all casting experts.

      Advert
      #245279
      David Cambridge
      Participant
        @davidcambridge45658
        Today I’ve had my first go at lost PLA aluminium casting. The results are very encouraging, but the casting is also far from perfect. In terms of mould making I think the technique works fine, but there is obviously something wrong with my casting technique or sprue setup. Can anyone offer any suggestions.
        David
        #245282
        Anonymous

          No scraping off the dross or degassing before pouring?

          Andrew

          #245284
          David Cambridge
          Participant
            @davidcambridge45658

            I did scrape of the dross. But didn't do anything with regards to degassing.

            David

            #245287
            frank brown
            Participant
              @frankbrown22225

              Flat horizontal surfaces can trap bubbles. Pre-warming the mould might help with this.

              Frank

              #245296
              Bazyle
              Participant
                @bazyle

                I think it was the bottom of the mould that went wrong with the full pressure head so not a venting issue, but it was the thinnest parts.
                Could it be rapid cooling of the first flow down the ingate getting solidified?
                Could some spec of plastic or other inclusion, even damp spec of dust that outgassed in the corner (though two corners so unlikely).
                Perhaps burnt residue of the plastic got swept down.

                Mostly I'm wondering if it was hot enough.

                #245297
                David Cambridge
                Participant
                  @davidcambridge45658

                  The mould was about 30 minute out of the fire, so it was probably at about one to two hundred centigrade inside.

                  I could see the corners before casting, and they looked to be good. And as you say, it was unlikely it would happen at both corners if it was fluke rather than systematic.

                  The aluminium (according to the thermocouple) was about 750 centigrade when I switched off the gas.

                  When you say 'Mostly I'm wondering if it was hot enough.' are you thinking about the mould or the aluminium ?

                  David

                  #245301
                  Peter Tucker
                  Participant
                    @petertucker86088

                    Hi David,

                    I think you needed venting at a couple of points, also (possibility) a shrink bob.

                    If you want much more in depth answers try here.

                    Hope this helps.

                    Peter.

                    #245306
                    John P
                    Participant
                      @johnp77052

                      Hi David,
                      First of all well done on producing a good casting,i think
                      these sort of problems plague would be casters i've had
                      more that enough over time.
                      Looking at the video at 1 min 36 the rounded form
                      may well be gas or even steam from the plaster
                      pushing back the metal, shrinkage normally has the
                      appearance of being more collapsed ie being pulled
                      from the inside ,yours looks pushed from the outside.

                      If you look at the Myford boy videos he has some very good
                      castings in nearly all of them the pouring and venting sprues
                      are extended in height allowing more of a head for the metal.

                      If you have the aluminium a 750 deg c i think you would be at the
                      upper end and could try to pour at a cooler temperature as the
                      sections you have for the sprues and the and the casting are
                      quite large.

                      In the photo in album Furnace and casting some small
                      lost wax castings and injected wax patterns ,aluminium
                      cast in investment powder flasks with vacuum assistance
                      as far as i can remember there was a 300 deg differential
                      between the metal and the flask temperature.

                      Keep on going your nearly there.

                      John

                      #245320
                      David Cambridge
                      Participant
                        @davidcambridge45658

                        Thanks everyone – lots of helpful suggestions (as usual!), encouragement, and a few things to think about over the next few days until I can try again!

                        http://www.alloyavenue.com looks really interesting, with lots of beautiful work!

                        David

                        #245328
                        Senior Yates
                        Participant
                          @senioryates

                          Hi David,

                          I spent 20 years in a aerospace foundry developing many rapid prototype methods and I bet your mold had plastic ash inside it. I would recommend burn out allow to cool down wash out and blow out with an air line then leave 24 hrs pre fire again when your happy there is no moisture left cast it. The early plastic Rapids gave us so much trouble with castings not forming, this is what we had to do. Long winded but you got all the ash out. Good luck I'm jealous of your set up.

                          Regards Senior

                          #245337
                          Ady1
                          Participant
                            @ady1

                            Read the Dan Calkin book a few years ago

                            A huge amount of detail and yet almost nothing on how the castings were done, and they had to be good

                            If memory serves only Dan knew the casting process to start with, he only ever shared it with one other person, and neither ever divulged their processes

                            —————————–

                            Dan had some clever  ideas for making castings
                            and wanted to keep these as trade secrets, so the
                            foundry area was off limits to all visitors.  One
                            thing Dan Calkin  did was to experiment  with
                            adding extra copper to the casting alloy. He found
                            that using an aluminum alloy with 5-10%  copper
                            in the casting alloy greatly improved the machin-
                            ability of the castings, while enhancing their
                            appearance.  Dan would weigh the aluminum to be
                            melted  and then added  a number of copper pen-
                            nies to the molten aluminum to get the desired
                            percentage.  At the Everett Street shop Dan usually
                            made all the castings himself  although  he some-
                            times shared the job with Dan Totten. All castings
                            used in all ELF engines were sand cast.

                            Edited By Ady1 on 04/07/2016 00:40:01

                            #245383
                            Neil Wyatt
                            Moderator
                              @neilwyatt

                              > He found that using an aluminum alloy with 5-10% copper in the casting alloy greatly improved the machinability of the castings

                              So he discovered Duralumin

                              Neil

                              #245396
                              Ajohnw
                              Participant
                                @ajohnw51620
                                Posted by Neil Wyatt on 04/07/2016 13:23:56:

                                > He found that using an aluminum alloy with 5-10% copper in the casting alloy greatly improved the machinability of the castings

                                So he discovered Duralumin

                                Neil

                                He might have used green or oil sand for a good finish. Especially with oil sand. 2nd hand info from some one who did lots of casting.

                                There is a DIY recipe for oil sand here

                                **LINK**

                                Not at all sure where the cancer warning comes from. Best stay away from bentonite and sand it seems.

                                The person who did a lot if it bought oil sand but only used a limited amount of it around the pattern.

                                John

                              Viewing 14 posts - 1 through 14 (of 14 total)
                              • Please log in to reply to this topic. Registering is free and easy using the links on the menu at the top of this page.

                              Advert

                              Latest Replies

                              Home Forums General Questions Topics

                              Viewing 25 topics - 1 through 25 (of 25 total)
                              Viewing 25 topics - 1 through 25 (of 25 total)

                              View full reply list.

                              Advert

                              Newsletter Sign-up