Acrylic processing technologies

Processing extruded acrylic sheets.

Extruded acrylic (PMMA) sheets can be processed on woodworking machines or on metalworking machines (cutting, milling, turning, drilling), and can also be sanded and punched with any suitable tools.

Cutting

In most cases extruded acrylic is cut with a circular saw for straight cuts and a band saw or router for other cuts. Laser cutting can also be used.

For better results, high-speed equipment is preferable. A high cutting speed combined with a minimal feed rate produces a clean edge. For the best result, make sure chips are removed and heat is dissipated, and provide cooling if necessary.

Extruded acrylic can be cut with high-speed circular saws at a blade speed of 4000 rpm. Use blades 250 mm in diameter made of high-speed steel or tipped with hard alloy; to avoid deformation, the saw teeth should have no set.

Standard equipment is used for milling. The best results are achieved with machines using small-diameter cutters and a high spindle speed (over 1000 rpm). Chip removal must be provided.

Recommended speed depending on blade diameter:

Drilling is done on a bench or portable drilling machine using special drills for light metals made of high-speed steel, high-performance high-speed steel or carbide, specially sharpened for drilling extruded acrylic.

It is recommended to grind the cutting edge of the drill parallel to its base; make sure the edges of the drilled hole are smooth to prevent cracking

During storage, extruded acrylic absorbs moisture from the air, which can cause bubbles to form during heat treatment.
The material should first be dried in a convection drying oven at 75-80 °C for 1-2 hours per mm of thickness. As a rule, even with a high moisture content, 24 hours of drying is enough.
Extruded acrylic is formed using established techniques (vacuum forming, pressure forming, press forming in a mould) in the temperature range of 130-140 °C.

Minimum heating temperature, °C: 120
Maximum heating temperature, °C: 145
Recommended range, °C: 130-140
Heating time: 3 minutes per 1 mm of material thickness

Formed extruded acrylic parts must be cooled evenly and not too quickly, so that no internal stresses build up. Leave the part on the mould until it has cooled to 60-70 °C.

Formed parts should be annealed to relieve stresses before they come into contact with solvents, paint or adhesive tape.

Avoid overheating or overcooling the part and the mould, high stretching speeds, excessive air pressure, and contact between the sheet and the mould before forming at high temperature.

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Machining or local heating can cause internal stresses. They can be almost completely eliminated by placing the material in a convection oven at an air temperature of 70 °C. The annealing time depends on the material thickness (for 3 mm, at least 2 hours)

Extruded acrylic sheets can be bonded to each other and to other materials, producing a strong and durable joint. Before bonding, heat treatment is advisable (to drive off moisture and relieve stress in the material).

Adhesives for bonding acrylic:

- solvent-based adhesive: a solution of polymethyl methacrylate in a volatile solvent;
- polymerising adhesive: PMMA syrup containing dimethylaniline, to which a polymerisation initiator (benzoyl peroxide) is added at the moment of bonding;
- other adhesives: epoxy, polyester, polyurethane, etc., grades AK-90, MP-88;81;BF-2(4,6);
- solvents: dichloroethane, methylene chloride.

Once the adhesive has dried and set at room temperature, annealing for 2-5 hours at 60 °C is recommended

Cut edges and matt surfaces can be polished to a high finish with a polishing wheel and polishing paste.

Clean the surface of the material with warm water and a mild, solvent-free detergent