In the undertaking of this task there were several skills new to me. The first part of the task was to design the mould for using in the casting process. This was done using 2D Design, a CAD program many schools use and that a lot of students will be familiar with. Drawing the basic shapes for the mould design was relatively simple but to output the design for CNC milling some extra knowledge was required. With some advice from the technician and a crib sheet of instructions to follow, the drawing was set up with the correct fill areas, line thicknesses, colours and layout for successful milling.
The milling itself was a case of making sure the output settings were correct for the relevant CNC machine, the blank mould was correctly prepared and the tooling in the machine was correct. Some of this was pre-prepared by the technician as the equipment and tooling is expensive and easy to break if set up incorrectly. This would be sensible to replicate in an ordinary classroom situation to save time and potential expenses. When everything was set up correctly, the milling was started and it was just a case of watching the process to ensure no errors occurred.
The overall time it took to complete the design and milling was quick and fairly simple, certainly achievable by KS3 students and above. If students were make to the moulds by hand, it would take a lot longer and results would be of a lower standard compared to the excellent and consistent output of using CAD/CAM. Once the design has been completed with CAD it is there forever so multiple moulds could be made to exacting standards; this repeatability is great for the classroom as if errors occur a new mould could be made with CNC in just a few minutes. We used MDF as the base material for our moulds; a cheap and readily available material but this also has some limitations. The inside layers of MDF can be quite fragile so when the part is removed from the mould after casting, small details of the mould can come away meaning a new mould would have to machined for re-casting. The mould I designed was quite robust and was completely intact after casting but the technician informed me that the best they have achieved from one mould was four casts.
Using CAD/CAM to produce the moulds also gives the opportunity to highlight links to industry and mass production - something a teacher could use in the classroom to give perspective to the task or set as a research homework for students to include in their write up. This could particularly useful for cross-curricular links as pewter has a great history in this country with a flourishing industry.
The casting process as described on the sheet above was very simple quick, enabling a finished product (bar cleaning up) to be manufactured in a few minutes. This means that for a class of 25, this task could possibly be completed in two lessons. Students learn about CAD/CAM, use some basic hand skills (filing and sanding) and learn how to melt and cast pewter so this is a well-rounded project to undertake. As with everything, there are limitations to how pewter casting could be used in schools. These would mostly be the complexity of the moulds produced and the equipment available to use. These factors would have major bearings on the time it would take to complete the task, always an issue in schools! If there was a knowledgable technician on hand to help the teacher, such as we had, this would be a great help in organising and executing the project.
Health and safety is, of course, a consideration for pewter casting as high temperatures, naked flames and tools are involved. The pewter used these days is safe in relation to that used pre mid-1700's which contained poisonous lead; it now consists of tin, copper and antimony. Pewter casting is safe enough for KS3 students to undertake as long as they are made aware of the hazards, provided with the correct protective equipment and have sufficient supervision.
As pewter casting in schools may be the only chance for a student to learn about forming metal, it is important for a teacher to raise awareness of the possibilities of the process with relation to what products can be made and careers that it might be involve in. Pewter casting can be used for jewellery making, a common topic in Design and Technology in schools, sculptures, tankards and trinkets to name a few products. If given the chance to cast pewter, a student may develop a deeper interest that could lead to career ideas in the future.
For more information on pewter casting in schools and in industry follow the links in this sentence.
No comments:
Post a Comment