Zeta Vacuum Forming Molding Machine Vacuum Model Former Dental Lab Equipment Orthodontic Retainers Maker 5'x 5' Thermoform Splint Small Vacu-Form Machine US Stock 5.0 out of 5 stars 1 $164.00 $ 164. 00 ($164.00/Count). Vacuum forming is a simplified version of thermoforming, where a sheet of plastic is heated to a forming temperature, stretched onto a single-surface mold, and forced against the mold by a vacuum. This process can be used to form plastic into permanent objects such as turnpike signs and protective covers.

Vacuum forming is a simplified version of thermoforming, where a sheet of plastic is heated to a forming temperature, stretched onto a single-surface mold, and forced against the mold by a vacuum. This process can be used to form plastic into permanent objects such as turnpike signs and protective covers. Normally draft angles are present in the design of the mold (a recommended minimum of 3°) to ease removal of the formed plastic part from the mold.

Relatively deep parts can be formed if the formable sheet is mechanically or pneumatically stretched prior to bringing it into contact with the mold surface and applying the vacuum.^[1]

Suitable materials for use in vacuum forming are conventionally thermoplastics. The most common and easiest to use thermoplastic is high impact polystyrene sheeting (HIPS). This is molded around a wood, structural foam or cast or machined aluminium mold, and can form to almost any shape. This high impact material is hygienic and capable of retaining heat and its shape when warm water is applied and is commonly used to package taste and odor sensitive products.^[2] Vacuum forming is also appropriate for transparent materials such as acrylic, which are widely used in applications for aerospace such as passenger cabin window canopies for military fixed wing aircraft and compartments for rotary wing aircraft. Vacuum forming is often used in low-level technology classes for an easy way to mold.

Modern vacuum-forming equipment is based on a series of US patents awarded in 1950, 1964, and 1974.^[3]

Typical applications[edit]

Original equipment manufacturers (OEMs) utilize heavy gauge vacuum formed components for production quantities in the range of 250–3000 units per year. Vacuum-formed components can be used in place of complex fabricated sheet metal, fiberglass, or plastic injection molding. Typical industry examples besides product packaging include: fascias for outdoor kiosks and automated teller machines, enclosures for medical imaging and diagnostic equipment, engine covers in a truck cab or for construction equipment, and railcar interior trim and seat components.^[4] Vacuum formers are also often used by hobbyists, for applications such as masks and remote control cars.

Common problems[edit]

There are some problems encountered in the vacuum forming process. Absorbed moisture can expand, forming bubbles within the plastic's inner layers. This significantly weakens the plastic. However, this can be solved by drying the plastic for an extended period at high but sub-melting temperature. Webs can form around the mold, which is due to overheating the plastic and so must be carefully monitored. Webbing can also occur when a mold is too large or parts of the mold are too close together. Finally, objects that are formed often stick to the mold, which is remedied by using a draft angle of three degrees or more in the mold.

Types of molds[edit]

There are numerous patterns one can make with vacuum forming. The most inventive way to use vacuum forming is to take any small item, replicate it many times and then vacuum form the new pattern to create a more cohesive form. The vacuum forming helps tie the individual pieces together and make one mold out of many pieces that can easily be replicated. From there plaster, concrete, etc. can be cast into the plastic form.

Wood patterns are a common material to vacuum form as it is relatively inexpensive and allows the customer to make changes to the design easily. The number of samples that one is able to get from any pattern depends on the size of the part and the thickness of the material. Once the specifications of the part have been met, the pattern is then used to create a ceramic composite mold, or cast aluminum mold for regular production. Potentially, there are ways to create holes in plaster with a vacuum form if the replicated forms made from the vacuum form are deep enough and gaps are left between them for the plastic to form into. Then, once the plastic is used to cast a plaster mold, the deep plastic areas will leave holes if the mold is not completely filled.

Castaluminium molds are cast at a foundry and typically have temperature control lines running through them. This helps to set the heat of the plastic being formed as well as speed up the fabrication process. Aluminium molds can be male or female in nature, and can also be used in pressure forming applications. The main drawback with this type of mold is the cost.

Machined aluminium molds are like cast aluminium, but are cut out of a solid block of aluminium using a CNC machine and a CAD program. Typically, machined aluminium is used for shallow draw parts out of thin gauge material. Applications may include packaging and trays. Cost is a significant factor with this type of tooling.

Composite molds are a lower cost alternative to cast or machined aluminium molds. Composite molds are typically made from filled resins that start as a liquid and harden with time. Depending on the application, composite molds can last a very long time and produce high quality parts.

Finishing methods[edit]

Once a vacuum forming has been created out of a sheet of plastic, a finishing operation will be needed in most cases to turn it into a usable product. Common vacuum forming finishing methods include:

Guillotining: The product is cut out of the sheet by pressing a blade through the product into a die underneath. This is a clean way of removing vacuum formed parts from the material sheet. It doesn't require a special cutting tool to be made for an individual product and is therefore suitable for low volumes of parts where straight lines are no problem. Cutting only straight lines and being a fairly slow approach compared to other finishing methods, guillotining can be expensive for projects with larger, more complex quantities.^[5]

Drilling: If simple round holes are the required finish, manually drilling them is a good solution for small quantities. Drilling guides can be used to ensure holes can be drilled quickly in the right place. As this is a labour-intensive method, it is only suitable for small production quantities.

Roller cutting: Process whereby the vacuum formed product is placed on a custom made cutter and pushed through a roller cutter machine. An efficient way of cutting vacuum formed items from the original sheet of vacuum forming material. The cutter can also cut any necessary holes, such as cable or access holes, at the same time. Roller cutting is suitable for fairly large items, where precision alignment is not required. As the vacuum formings and the cutter are rolled sideways through the roller cutter machine, some misalignment can occur. Roller cutting can't be used for making holes or features in the sides of vacuum formings, as the cutter tool always cuts vertically from the bottom.

Press cutting: This is a very precise method of cutting which uses a press and a custom precision made cutting tool. This method is very suitable for items where the roller cutter process wouldn't achieve the precision required. It is often used for punching very small finished items out of a plastic sheet, rather than punching features into a product. Press cutting can't be used to make features in the sides of vacuum formings.

Cutting with a CNC machine: Machining is a very precise method of creating holes & features. The real advantage is that it can be used to create features in the sides of vacuum forming, e.g. guide rails for a tray that needs to slide onto shelving. It can also cut sidewalls of a different depth than the pockets—something which cannot be done with roller or press cutting.^[6]

References[edit]

1. ^J.L. Throne, Understanding Thermoforming, Hanser Gardner Publications, Inc., Cincinnati, OH, 1999
2. ^Plastics, Eagle (2013-02-18). 'High Impact Polystyrene Sheeting (HIPS), What is it?'. Eagle Plastics Ltd. Retrieved 2018-04-30.
3. ^'Vacuum Forming History - Display Developments'. www.displaydevelopments.co.uk. Retrieved 2020-01-25.
4. ^'Vacuum Forming Services - Custom Vacuum Forming Plastic | Emco Industrial Plastics'. www.emcoplastics.com. Retrieved 2018-04-30.
5. ^'Vacuum Forming - 5 Finishing Methods'. www.toolcraft.co.uk. Retrieved 2018-04-30.
6. ^Webster, Stephen. Vacuum Forming Market, Stephen Webster Plastics Ltd. Retrieved 2018-04-30.

Further reading[edit]

• Soroka, W. Fundamentals of Packaging Technology, IoPP, 2002, ISBN1-930268-25-4
• Walsh, D. E. Do It Yourself Vacuum Forming for the Hobbyist (rev. ed.), Workshop Publishing, Lake Orion, MI, 2002, OCLC46798883
• Yam, K. L. Encyclopedia of Packaging Technology, John Wiley & Sons, 2009, ISBN978-0-470-08704-6

A Low Cost Vacuum-Forming System

James P. O'Leary, M.S. James P. O'Leary, M.S. Associated with the Rehabilitation Research and Training Center #7, Tufts University School of Medicine, Boston, Massachusetts.');'>*
Edward A. Bianchi, B.S. Edward A. Bianchi, B.S. Associated with the Rehabilitation Research and Training Center #7, Tufts University School of Medicine, Boston, Massachusetts.');'>*
Richard A. Foulds, M.S. Richard A. Foulds, M.S. Associated with the Rehabilitation Research and Training Center #7, Tufts University School of Medicine, Boston, Massachusetts.');'>*

This work was supported in part by Rehabilitation Services Administration Grant #16-P-56800/1-10 (RT-7).

Vacuum-forming is an excellent method for molding sheets of plastic into complicated shapes. It is just beginning to be used in the field of rehabilitation medicine where the need to make devices that fit the human form is great. This article describes a new, inexpensive apparatus which enables orthotists and prosthetists to use the vacuum-forming process in their work with a very small outlay of capital. Very little training is required to use the apparatus, and it is now being made available in limited quantities.

In the vacuum-forming process a sheet of hot, pliable plastic is drawn either into or around a mold with the use of suction provided by a vacuum pump. When the plastic cools and hardens, it retains the shape caused by the mold. An example of the usefulness of a molded orthosis is shown in Fig. 1.

The process, though simple, when adapted to the needs of mass-production, requires very expensive machinery. Until recently only industrial vacuum-forming equipment was available, with prices ranging from $4,000 to over $125,000. Because of the large investment in money and space required to obtain and use the machines designed for mass production, very few medical facilities have made use of the vacuum-forming process.

For mass-production expensive equipment results ultimately in low unit costs. But for the specialized, one-of-a-kind world of rehabilitation, expensive equipment does not necessarily justify itself, and a low-volume, low-cost, non-automated system seems much more suited to the needs of orthotists and prosthetists. Such a machine is feasible when the inherent simplicity of the vacuum-forming process is fully exploited.

With these thoughts in mind we designed and built a vacuum-forming apparatus called the 'Bracemaker' (Fig. 2 ), which is simple, functional, versatile, and, above all, inexpensive. In accordance with the terms of the federal grant which provided part of the funds for this work, we are making the design of the 'Bracemaker' available to the medical community.

Why should orthotists and prosthetists be interested in vacuum-forming, when they already have many conventional techniques to use? The advantages of plastics are part of the reason. Plastics are often found in rehabilitation devices where light weight, cosmesis, flexibility, durability, and close fit are needed. Until recently, it has been necessary to form plastics by hand, a process that requires considerable skill, and often repeated attempts, to achieve good results on any but the simplest shapes. With vacuum forming very little skill is needed, results can be quite consistent, and parts can be formed which cannot be done at all by hand. Moreover, the technique can be used with a large variety of plastics— almost all of the thermoplastics. This eliminates the need for special, low-temperature forming plastics, and opens up a wide range of new plastics that are extremely useful in the provision of rehabilitation devices.

THE PROCESS

The type of vacuum-forming most useful in prosthetics and orthotics can be broken down into six distinct steps:

1. Mold Preparation—A mold in the shape of the part to be formed must be prepared. In prosthetics and orthotics plaster-of-Paris is usually the material of choice. The mold is placed on a special table (Fig. 2), and supported for the best wrapping action of the plastic.
2. Heating—The plastic sheet must be brought to a temperature that makes it soft and pliable, yet leaves it strong enough to resist tearing (Fig. 3 ).
3. Draping—The plastic sheet must be draped over the mold and then sealed at its edges, so that the mold is totally enclosed (Fig. 4 and Fig. 5).
4. Drawing—The air underneath the plastic is pumped out, allowing the pressure of the atmossphere to wrap the soft plastic around the mold, taking its shape (Fig. 6).
5. Cooling—The plastic is allowed to cool while the vacuum is maintained. The plastic hardens and regains its normal properties.
6. Extraction—The finished part (Fig. 1, left) is cut out of the plastic. (Unfortunately, the excess plastic is waste which can rarely be reclaimed, even though it is inexpensive relative to other materials). The mold may also be removed at this time. Usually it can be removed intact, but ocas-sionally it must be broken and removed in pieces.

Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6

THE BRACEMAKER

The basic elements of the 'Bracemaker' vacuum-forming system (Fig. 2) are:

1. an oven, for heating the plastic
2. a rack, for handling the plastic
3. a vacuum table, to support the mold and seal the plastic against air leakage during drawing
4. a vacuum pump, for withdrawing the air

The oven is an ordinary household oven, either gas or electric. Because they are mass-produced, these ovens are far less expensive than the acceptable alternatives. Yet, they are just as adequate as laboratory and industrial ovens are for this purpose. One can often be bought new for $200.00 or less.

The rack (Fig. 7 ) has been designed especially for the vacuum forming process, and it holds the plastic sheet firmly about its perimeter even when the plastic is in the molten stage. Its special clamping devices, or 'traps' (Fig. 8 and Fig. 9), are designed to permit easy insertion and removal of the plastic, and to obviate the need for special preparation of the plastic, such as drilling holes for bolts or pins. The spring-loaded continuous hinge digs into the plastic when tension is applied to pull it out. The traps must be released by hand, as shown in Fig. 8, in order to free the plastic sheet. One end of the rack is removable to permit insertion of the sheet. To heat the plastic, the rack can be placed in an oven instead of one of the regular wire shelves. This arrangement makes it possible for the plastic to be placed in the oven, removed, and carried to the vacuum table without the need for handling the plastic itself. Because the plastic sags several inches when heating, and becomes sticky and pliable, this handling ability is quite necessary for success.

The vacuum table, also a special piece of equipment, is the basic work-surface of the 'Bracemaker.' It is a low table, designed to sit atop a workbench. It incorporates a perforated surface on which the mold is placed and through which the air is withdrawn, a rim or vacuum seal which provides a seal against leakage (Fig. 9 ), a valve to control the rate at which the plastic is drawn around the mold, and a set of guides to aid in draping the plastic over the mold.

The vacuum pump is nothing more than a simple household vacuum cleaner with fittings to attach the suction hose to the vacuum table. Surprisingly, it is more than adequate for the job, and in fact is far better than vacuum pumps costing four to twenty times as much because a vacuum cleaner pump has a far greater tolerance for leakage than most other pumps, while still being able to draw the vacuum needed.

The peripheral equipment needed varies with the raw material used and the end product desired. Tools for cutting out sheets of raw plastic, smaller cutting tools for extraction work, cast cutters, finishing tools, are all needed to some extent in vacuum-forming. But there are many different tools which can do these jobs, and most shops have a number of suitable tools already. For this reason such items are not supplied with the 'Bracemaker,' but recommendations as to what is needed and what can be used are available.

OPERATION

A good example of the use of vacuum forming in orthotics is the procedure used to make an ankle-foot orthosis (AFO). Fig. 1 shows a conventional steel-and-leather orthosis on the right and a vacuum-formed plastic orthosis on the left. This type of plastic orthosis is, to date, the most widely used and highly developed of the vacuum-formed appliances.

The ankle-foot orthosis is usually made out of polypropylene sheet, most often 3/16 in. thick. Polypropylene is often called an 'engineering plastic,' and is noted for its ability to stand up to constant flexure, its resistance to 'creep,' its strength, its springiness, and its low cost. These are all useful properties for the AFO. Other useful available plastics are Lexan, ABS, and polyethylene. The cost of plastic for each brace varies with material and supplier, but, at the time of this writing the average cost in the Boston area for polypropylene for one orthosis is $4.00.

To make the mold for the AFO, a plaster cast of the patient's lower leg and foot is taken, using standard techniques. The cast is then cut down the anterior wall with a cast cutter, and removed from the patient. It is then dusted thoroughly inside with talcum powder, sealed again usually with strips of plaster bandage, and filled with plaster of Paris.

When the plaster has cured, the cast is stripped away, to reveal a positive model of the patient's lower leg and foot. This model is finished to remove rough spots, and then trimmed at the toe and shin so that it will stand heel upwards on the vacuum table (Fig. 2 ). The mold is then covered with cotton stockinet, and placed on the vacuum table.

Vacuum Forming Plastic

A sheet of plastic is placed in the rack. The rack and plastic sheet are then inserted in the oven, which has been holding at 500°F. The rack should be placed in the top of the oven, with plenty of clear space underneath to permit the plastic to sag as it is heated. Within five minutes the plastic will begin to turn clear and sag. In two or three more minutes it will be clear all the way to the edges of the rack, and it will have sagged six to eight inches in the center. At this point it is ready to be removed from the oven (Fig. 3 ).

The vacuum pump is turned on, and the vacuum control valve is opened to one quarter-turn. The rack containing the heated plastic is removed from the oven, carried to the vacuum table, lifted high over the mold, and draped smoothly down over it (Fig. 4 ). The rack is pressed down onto the table (Fig. 5 ), stretching the plastic over the rim which surrounds the vacuum surface, and forming the vacuum seal (Fig. 9 ). The plastic will begin to draw down over the mold, and the rate of draw can be adjusted by further opening or closing the vacuum valve. Once the plastic is properly drawn down, the valve should be adjusted so that it does not draw further, but still remains tight on the mold (Fig. 6 ). The vacuum is left on until the plastic hardens—in two or three minutes.

Once the plastic has cooled thoroughly, it can be removed from the rack. The orthosis can then be rough-cut out of the plastic, and the mold removed. (The mold can normally be re-used, should that be necessary.) The orthosis is then finished to the proper shape, but left a little oversize at the ankle. The ankle area is where the orthosis flexes the most, and the size of this section is critical to the corrective force the orthosis provides to the patient. It is necessary to leave the ankle stiffer than is thought to be necessary, so that material can be trimmed away during patient trials until the correct amount of stiffness has been reached.

A strap with a Velcro closure is riveted at the top of the orthosis, so it can be fastened to the patient's leg (see Fig. 1). The lower part of the orthosis inserts into the patient's shoe as if it were part of his foot. No other attachments are necessary.

Plastic Vacuum Forming Machine

Should the patient find the orthosis to be irritating at some point, or some other flaw is discovered, minor changes in the orthosis can be made. Small areas of the plastic can be re-heated with an electric heat gun or a propane torch, and bent by hand to a new configuration. However, major modifications by this method are rarely successful, and usually a new molding is required.

The final finishing of the orthosis should include fire-polishing. This process extends the life of the orthosis by removing microscopic cracks left on its edges by previous finishing operations. These cracks are where the stresses in the plastic become highest, and where breakage is most likely to start. Playing the blast (but not the actual flame) from a propane torch along the edges of the brace will cause a small amount of plastic to melt there. When the melted plastic cools it forms a smooth bead, which should be devoid of cracks.

Make Money With Vacuum Forming

PROJECT STATUS

In May of 1974 we began the distribution of a small number of pre-production 'Bracemakers' to hospitals and brace shops in the New England region and in New York. The object was to test the machine in the field and to gain a base of experience outside of our own facilities. As of this writing we have had machines in the field and in operation for over a year, with encouraging results. We estimate over three hundred orthoses have been made on our machines. Most of these have been AFO's, but a number have been experimental orthoses of other varieties. The private orthotics facilities using our machine have shown a definite ability to custom-manufacture plastic orthoses.

Our future plans for the 'Bracemaker' project aim at the development of a self-perpetuating technology. This includes the development of a production model of the 'Bracemaker,' the distribution of machines to facilities throughout the country, and the establishment of a clearinghouse for the assembly and distribution of information on vacuum-forming. In addition, we intend to continue our research into new uses for vacuum-formed parts in rehabilitation medicine.

Make Money With Vacuum Forming Machines