Machining PMMA-GS

PMMA belongs to the amorphous thermoplastics and therefore has no defined melting point, but softens above the glass transition temperature (around 110 °C). The cast variant GS is polymerised between glass plates in a cell-casting process. The resulting high molecular weight gives GS a higher heat deflection temperature, better chemical and stress-crack resistance and excellent suitability for polishing and machining – even in large thicknesses. PMMA is stiff, hard and crystal-clear, yet brittle and notch-sensitive.

PMMA-GS machines excellently – milling, turning, drilling and sawing produce clean, dimensionally accurate results, even on thick-walled parts. We also offer polishing (high gloss), bonding and thermoforming. Because of its brittleness and stress-cracking sensitivity, we use sharp tools and adapted cutting parameters and avoid aggressive coolants. This is how we reliably produce transparent precision and visual parts – from single pieces to series production.

PMMA-GS is worthwhile whenever transparency and weathering resistance must be combined with demanding machining, higher temperature or chemical resistance – for example:

• Thick-walled, machined and polished viewing and display parts
• High-optical components, light guides and displays
• Model, pattern and mould making
• Thermoformed hoods, covers and glazing
• Applications with slightly higher temperature or chemical loads than XT

PMMA-GS is a premium grade and usually more expensive than extruded PMMA (XT), but still below high-performance engineering plastics. As a rough guide, semi-finished stock prices are in the range of about 6–15 €/kg. The component price is determined mainly by the semi-finished shape and dimension, material utilisation (offcut), machining effort and lot size. We are happy to quote binding prices on request based on your drawing. Note: for thick, machined or high-optical parts GS is usually the better choice; for thin, laser-cut blanks the cheaper XT.

Equally important are the limits of the material:

• Impact- and shatter-resistant applications – PMMA is brittle; use polycarbonate (PC) for high impact strength
• Contact with solvents, alcohols or aggressive cleaners (risk of stress cracking)
• Continuous service above about 80 °C – then use more temperature-resistant materials
• Components with fire-safety requirements – PMMA is only normally flammable (B2 / UL 94 HB)
• Thin blanks with tightest thickness tolerance or laser cutting – then extruded PMMA (XT)

An honest assessment – and how the disadvantages can be mitigated in practice: Advantages:

Disadvantages:

Practical tip: PMMA-GS plays to its strengths wherever transparency and optics meet demanding machining, thick cross-sections or slightly higher temperatures. For thin, laser-cut blanks the cheaper XT is more sensible; where shatter and impact resistance are the priority, we recommend tough polycarbonate (PC).

• Crystal-clear with about 92 % light transmission, non-yellowing
• Very good weathering and UV resistance
• Higher heat deflection and chemical resistance than XT
• Excellent machinability and high-gloss polishing (also thick parts)
• Hard, high-gloss surface; suitable for food contact
• Brittle and notch-sensitive – low impact strength (not shatter-proof)
• Sensitive to solvents, alcohols and esters (stress cracking)
• Continuous service limited to about 80 °C
• Greater thickness tolerance and higher price than XT; only normally flammable (B2 / UL 94 HB)