Vacuum Forming Moulds or Plastic Fabrication? Specialisation in making vacuum form moulds or tools has been the keystone of the growth of APH over many years. Often clients with requirements for plastic components have approached us with a preconceived idea that plastic fabrication is the solution to...
Vacuum forming machines made simple
You can now make your own vacuum forming machines, using house hold items such as a vacuum cleaner, kitchen oven, if you want to know more about making your own vacuum forming machine, contact APH WEB
Vacuum Forming Moulds or Plastic Fabrication?
Specialisation in making vacuum form moulds or tools has been the keystone of the growth of APH over many years. Often clients with requirements for plastic components have approached us with a preconceived idea that plastic fabrication is the solution to their problem.
Of course APH can offer fabrication in a range of plastics, but frequently Acrylic is the material of choice, due to its availability in many colours and thicknesses and its robustness when assembled. This can usually mean bonded joints, mechanical joints either bolting or even slotting one part into another. Point of sale items, are often made in this way, but at APH we have employed plastic fabrication to produce scale models, model display stands/cases etc.
But back to the original question that customers would ask, how much will it cost to fabricate a few prototype or production parts. The advice given would depend upon the shape of part or parts and the material flexibility, in fact vacuum forming would offer more choice in materials than those suitable for fabrication. But more often than not, the shape would lend itself to vacuum forming, maybe with slight changes to the corner radii, angle of sides or thickness or type of material. With few comprises their parts could have a very low cost vacuum forming mould hand made or machined in wood or MDF. From such a mould their quantity requirements would be met to a production quality finish without seams as in fabrication and the advantage of production intent surface textures, like haircell or pinseal. From the vacuum forming moulds, the part will need trimming of excess material, which again offers more complexity in shape than plastic fabrication could achieve. Sometimes a combination of the two processes will be utilised. The customers shape may be best made, by bonding a plastic fabrication with a part from vacuum forming. This could be described in simple terms, say a rectangular tube 200×200x400lg (fabricated) with a domed closure bonded to one end or both(vac. formed). With ABS using very specific adhesives like MEK achieves a seamless parent material like join between fabrications and or vacuum form part.
Here are a few questions and answers you would ask an vacuum forming expert and here are the answers that you should expect to receive.
Q. What is vacuum forming?
A. Vacuum forming is using a vacuum to pull heated and softened plastic sheet’s over a tool which thereby forms a part.
Q. How does vacuum forming work?
A. Tooling that matches the inside surface of the part, is fixed to a vertically moving platform. From this, a plastic sheet is clamped in a pivoting frame above the tool which then allows the top heaters to slide over onto specific rails to soften the plastic. Which can then be moved back to allow air be blown and pre stretch the sheet. The tool platform is raised, then applies the vacuum which sucks & forms the softened plastic over the tool. When this is all completed, it is then cooled, from this the tool is lowered with a little air pressure, the clamp frame is raised and part removed for trimming.
Q. Is my design suitable for vacuum forming?
A. If your design does not have too many undercut areas, fine raised/recessed points, or very large section changes which makes the draw too deep then your design can be vacuum formed.
Q. Is vacuum forming a low cost way to make my part ?
A. Vacuum forming is considered the cheapest method to produce parts for low to medium volumes, this is mainly because of the low cost tooling.
Q. What tolerances can be held?
A. The tooling dependent and material choice, however +/- 1mm is realistic Although some area’s it might be held to +/- 0.5mm.
Q. What material thickness can be vacuum formed?
A. Almost any thickness given could be formed, although typically 1 –5mm
frequently used.
Q. Does the material get thinner during forming?
A. Yes thinning of your desired material will always occurs, therefore early input by us on part design if possible, will ensure that the changes in feature are kept to a minimum and that the feature flow is as best they can do it.
Q. What is the surface finish like?
A. The surface finish will depend on a number of issues. These are where it includes complexity of a part, thickness of the material, gloss level of material chosen, heat required to form part and design and finish and venting of tool. However generally surface finish is very good and fault free.
Q. What plastic materials can be formed?
ABS smooth or embossed. HIPS, PVC, PP, HDPE, CPS, CHD, PC, including Lexan and Kydex. PETG which covers almost every product requirement from fire retardancy to electrical conductivity.
Q. Can 2D drawings or sketches be used to make tooling?
A. Yes, however it will depend upon the part design on 2D drawing to determine if it can be machined or hand made. In many cases if would be more likely hand made. Where as, if the part is seen to be more complex, we can offer conversion to CAD 3D data as a priced service.
Q. What CAD files should I supply?
A. Iges data is preferred, however at cost we can get Catia and other native CAD data translated for use on our CADCAM. Our CAD stations operate Unigraphics.
Q. Why do the sides of part have to be tapered?
A. Vacuum forming requires a taper on side faces of about 2-3 degrees, this helps the forming and flow of material, but more importantly is essential to be able to withdraw the tool from the moulding.
Q. Can deep features be formed?
A. Yes deep features can be formed. However, this is as long as they have required taper and do not thin the material too much. To ensure the sharpness of features a plug assist is sometimes used, this pushes onto the opposite side to the vacuum and can be manually applied or by machine adaption.
Q. Is tooling expensive?
A. Vacuum form tooling is not expensive, making it cost effective for prototype quantities and low to high volume production. Tooling can be made in wood and MDF for basic proto feasibility parts. CNC machined resin board tooling, allows for finer tolerances and detail to be achieved and will be able to last to produce potentially, thousands of parts. Aluminium tooling offers the optimum solution to surface finish, texturing and part volume capability.
Q. What is maximum size part that can be formed?
A. Any size is limited by the common max sheet size of 2240×1220. Vacuum form machines can produce several or one part per time in this sheet, the bigger the machine then the deeper features can be achieved.
Q. Can holes and cut outs be added?
A. Yes holes and cut outs can be made, we produce all routing, trimming fixtures and jigs needed to add all production features to your components. The edges will be smoothed and free of burrs as much as possible.
Q. What quantities can be produced with vacuum forming?
A. When using MDF tooling it maybe a couple of hundred. With resin board tooling it maybe a few thousand. Then looking at aluminium tools , it will be capable of many thousand and last the product lifetime.
Q. How soon could I have parts from order?
A. First parts are limited due to the completion of tooling, which depends upon the quality of CAD or Drgs received. Vacuum forming is not a fast process like injection moulding; the cycle time is slower due to the generally non-automated nature needing an operator dedicated to the machine. However, typically first off parts would be available 3-4 weeks on receipt of an order.
Vacuum forming machines,tooling & processes
Vacuum forming machines consists of a single or double heating element, frame for holding the plastic, moving platen or table to hold the tool or pattern used to make the shape of the part you wish to produce and a vacuum tank.
The heaters are usually at the back of the vacuum forming machine and the clamping frame and platen at the front. The platen sits within the frame and can be moved up and down, whereas the clamping frame is in a fixed position for holding the plastic over the tool during the moulding process. Some vacuum forming machines are manually operated and others are semi automatic or fully automatic.
The object of each type of machine is the same in that they all heat plastic materials until soft enough to mould over a tool, pattern or mould, under vacuum. When the plastic is under vacuum, the suction achieved is around 28 HG about 1% less than what might be considered as ultimate vacuum.
The tool can be made using various materials providing that they are strong enough not to collapse when under vacuum. These materials include:- wood & MDF for prototype or low volume, through to resin tooling board or cast resins for mid volume parts, up to aluminium either machined or cast for high volume The latter would depend on depth of feature and thickness of material and hence heat required to soften material prior to forming. All tooling would be vented to vacuum side by small 0,5-1,0mm dia. holes around the tool and at key draw areas and features to pull the plastic to form over the tool.
The surface of the tool will reach around 60 to 80 degree’s when used in production. Various plastics require different temperatures to become soft enough to mould. * Materials such as High Impact Polystyrene and ABS plastics will soften at between 150/190 deg C and Polycarbonates at around 185/205 deg C*. The design of the tool is very important, you need to build into your design a draft or taper down the sides of 2 degree’s or more and add radii to all corners, the bigger the better for ease of forming.
There is a rough formula for moulding recesses or pockets that might be needed in the tool. The width and length of the recess should be twice that of the depth of the recess to allow the material to be drawn down into the pocket without the material becoming so thin that it splits when under vacuum. Once the tool has been designed and made with the all foregoing in mind, you are now ready for moulding.
The tool is fastened to a board, which is in turn fastened to the platen. The platen is lowered and a plastic sheet is placed onto the frame and clamped in position. The heater or heaters are brought over the plastic and left in position until the plastic becomes soft and pliable, timing is critical, so checking and recording for repeatable quality forming is essential. The heaters are then withdrawn and the tool brought up into the plastic, the vacuum switched on to suck the plastic around the mould to remove all of the air between the tool and the plastic, thus creating a replication of the surface of the tool. Whilst the vacuum is on, the sheet is cooled using fans and or compressed air until it becomes solid and retains its shape.
Once this has been done, the tool and platen can be dropped down and the plastic removed from the clamping frame ready for trimming to obtain finished part. You can mould as many parts as needed, providing that the tool has been designed and made using the right materials for the quantities required. * Information about mechanical properties of vacuum forming plastic materials and uses can be found on various plastic manufacturers web sites.
Welcome to the Vacuum Forming Blog
Here you will be updated about vacuum forming, and vacuum forming procedures, such as plastic fabrication and projects and moulds formed using vacuum forming machines and processes of vac forming, vacuum forming plastics and fibreglass and other materials and the process of designing prototypes and methods to mass produce products.
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