How to choose tooling boards

01 Four common types of tooling board

The main resin systems are epoxy, polyurethane and unsaturated polyester. Lightweight boards are also polyurethane, but their foamed structure gives them substantially different densities, hardnesses and applications from conventional modeling boards. They are therefore considered separately here.

Fine surface detail in lightweight board depends on small, uniform cells. Coarse-cell foam usually serves as internal support or a substrate. Board used at a model surface needs a fine, consistent structure to reduce filling and sanding after machining.

02 Consider epoxy first for heated tooling

Epoxy boards are the first choice for masters and molds that require elevated-temperature performance. Ambient-temperature models generally do not need that additional material cost: polyurethane, unsaturated polyester or lightweight boards can be selected by application. With epoxy tooling prepreg, however, cure compatibility matters even when the initial cure temperature is low.

Why use epoxy board for prepreg cured at about 140°F (60°C)?

A common low-temperature tooling-prepreg route is an initial cure at about 140°F (60°C) on the master, followed by demolding and a high-temperature post-cure. The master experiences only the initial cure temperature, which some polyurethane boards can withstand. That still leaves the question of whether the resin at the contact surface cures correctly.

Certain polyurethane boards and other isocyanate-cured systems can inhibit the interfacial cure of heat-cured epoxy prepreg. Toolmakers sometimes describe this as polymerization inhibition. Its occurrence depends on the board formulation, cure state and prepreg resin system. Heat resistance and cure compatibility are separate requirements.

For these epoxy tooling prepregs, an epoxy-board master is strongly recommended, together with a compatible sealer and release system. If polyurethane or another board is used, first validate the cure with the actual board, coating and prepreg combination.

Where only the initial cure at about 140°F (60°C) takes place on the master, an epoxy board with a Tg of about 230–266°F (110–130°C) is usually a useful starting point, balancing temperature margin and cost. If the composite mold stays on the master during high-temperature post-cure, select the master material against the highest temperature in the complete cycle.

03 Epoxy-board machining quality and dimensional stability

Master accuracy depends on stability after machining and dimensional changes during heating. Epoxy board also needs sufficient toughness and a fine, smooth machined surface to limit repair and finishing work.

1. Stability after machining. The board should retain its surface geometry and dimensions after roughing and finishing. For bonded blanks, adhesive cure and support arrangements must also be controlled to prevent warping.
2. Lower thermal expansion. Compare coefficients of linear thermal expansion over the actual working temperature range and estimate movement during the initial cure. This becomes more important as tool size and temperature rise increase.
3. Adequate toughness. Thin edges, small radii and holes should resist chipping during machining and cracking during heating, cooling and demolding.
4. A fine, smooth surface. Low surface roughness and small pores reduce filling, sanding and sealing work.
5. Good machinability. Smooth cutting, less dust and intact edges make it easier to produce a consistent surface, including across local repairs.

A machining trial should include the project's thin edges, deep slots, holes and curved surfaces, so that cutting behavior, edge integrity and surface quality can be assessed together.

04 Size and support considerations for direct epoxy-board molds

For small parts and short production runs, machining a mold directly from epoxy board can avoid the composite mold replication stage. Heat-resistant grades are available for consideration in processes at 248°F (120°C), 302°F (150°C) and 356°F (180°C). Suitability still depends on stiffness at forming temperature, dimensional movement, sealing and the required number of cycles.

HDT is the heat deflection temperature under specified loading and test conditions; Tg is the glass transition temperature. They describe different properties. These thermal indicators support preliminary selection; high-temperature stiffness, dwell time and pressure must also be checked when defining the forming cycle.

Heat resistance does not mean low expansion

Boards of this type often have a coefficient of linear thermal expansion around 40 × 10⁻⁶ K⁻¹, depending on grade, typically greater than aluminum and steel. Heating changes tool surfaces and hole positions; larger tools undergo greater movement.

Direct epoxy-board molds are therefore generally used for small parts with principal dimensions within 19.69 in (500 mm). This is a practical selection guideline, not an absolute limit; allowable size depends on temperature rise and part tolerances. Large or tightly toleranced parts are generally better served by machining a board master and reproducing it in a low-expansion composite mold.

Avoid extensive rigid bonding between board and steel plate

A steel plate can support the mold, but its thermal expansion differs from epoxy board. A rigid adhesive over a large area restricts relative movement during heating and cooling and can cause board warping, bond failure or local cracking.

A heat-resistant silicone adhesive can provide a flexible bond to the steel support, allowing the bondline to accommodate relative movement. Bond area, thickness and location must still meet loading requirements. Board-to-board joints instead use a compatible structural adhesive to preserve the blank's stiffness and machining accuracy.

05 Distinguish modeling boards from tooling boards for ambient-temperature use

Ambient-temperature applications fall broadly into models and working tools. Models support styling, assembly or color reviews; working tools must retain accuracy through repeated use. Their demands for abrasion resistance, load capacity and datum stability differ.

Polyurethane modeling boards

Polyurethane modeling boards are used for engraved prototypes, automotive verification models and color models. Engraved prototypes need intact patterns and small radii. Verification models check component fit, gaps and flushness; painted color models support shape and color evaluation.

PUBOARD 72 suits engraved prototypes for tire-mold manufacture. Its fine, uniform structure supports machining of patterns, curves and small radii, as well as local repair and modification. The prototype is subsequently used to reproduce the production mold; the board itself does not undergo high-temperature vulcanization.

PUBOARD 65 suits automotive verification and color models. Its density is 40.58 lb/ft³ (0.65 g/cm³), hardness approximately Shore D 63 and heat-resistance value 167°F (75°C). It is suitable for overall styling, component trial fitting and color review after painting.

PUBOARD 0780 suits high-quality verification models. Its density of 46.82±1.25 lb/ft³ (0.75±0.02 g/cm³) is higher than PUBOARD 65. It supports fine surface, edge and hole machining, and models subject to repeated assembly, measurement and handling.

Values are typical properties. Thermal indicators aid material selection; actual service temperature also depends on load and duration.

Verification models undergo component trial fitting, measurement and handling. Metal inserts can support threads and locating features that see repeated assembly; thin edges and clamping areas benefit from local reinforcement. Color models prioritize paint finish, so sealing, primer and sanding time should be included in the cost of board selection.

Three main uses of polyurethane tooling board

Polyurethane tooling boards provide working surfaces or locating datums. Select them according to the job: checking fixtures need stable references, foundry tools need abrasion resistance, and nickel-shell electroforming masters need dimensional control through temperature changes.

PUBOARD 1650 is an option for checking and holding fixtures. High-density board suits machining of contoured support and locating surfaces. Checking fixtures need stable datums; holding fixtures must also withstand clamping forces and locate repeatedly. Metal inserts, locating pins and baseplate support work with the board to maintain tool accuracy.

Abrasion-resistant PUBOARD 1350 or 1250 can be used for foundry patterns, pattern plates and core boxes. Repeated sand contact wears surfaces and edges, affecting subsequent sand-mold accuracy. Consider sand, molding or core-making methods, cleaning and cycle count; heated core-making requires a separate thermal assessment.

PUBOARD 1850 is an option for nickel-shell electroforming masters. Its high density and dense surface, with high filler content reducing thermal expansion, help control dimensional change during electroforming. After machining, prepare the conductive surface and validate contact with the electroforming bath and subsequent release.

PUBOARD 1850 has an HDT of 203±9°F (95±5°C) and a coefficient of linear thermal expansion around 41×10⁻⁶ K⁻¹ over 68–122°F (20–50°C). That coefficient applies to a specific test range. For electroforming above this range, evaluate dimensional movement at the actual process temperatures.

HDT means heat deflection temperature. The heat-resistance values and HDT in this table use different assessment methods; neither can be directly equated with continuous service temperature.

Advantages of polyurethane board in foundry tooling

Foundry patterns and core boxes must be machined accurately and retain their surfaces after repeated molding, cleaning and release. Polyurethane tooling boards combine detailed machining, dimensional stability and abrasion resistance. Compare the following factors when selecting them.

Uniform structure enables fine detail. Board has none of natural timber's grain or knots, giving more consistent cutting behavior on curves, small radii and patterns. Surface roughness, edge integrity and the machinability of repaired areas all affect subsequent replication.

Accuracy matters during both machining and use. Post-machining warping transfers to patterns and sand molds; temperature differences, loads and support also alter surfaces in service. Machine and inspect precision tools at a specified temperature, taking particular care over temperature differences on large tools.

Abrasion resistance governs accuracy after repeated molding. Hardness measures resistance to indentation; abrasion resistance concerns material loss through friction. They are not the same property. Long-term sand contact wears surfaces and edges. Compare abrasion data obtained by the same method, then judge service life against the actual sand, surface treatment and cleaning method.

Assess deformation and cracking separately. Elastic modulus affects deflection under working loads; compressive and flexural strength relate to load capacity; toughness affects cracking at thin edges and release features. Tools subjected to repeated compression should also be checked for residual indentation after unloading.

Release and surface treatment affect long-term use. Release agents, core binders and cleaning methods can affect boards or bondlines. During trials, inspect surfaces and edges after repeated release and establish whether cleaning accelerates wear.

Final casting accuracy depends on several process stages. Pattern dimensions, casting shrinkage, release deformation and machining allowance must share the casting's tolerance budget. Allow for casting shrinkage while also controlling the board's own dimensional movement.

Board serves foundry masters and related tooling; it does not contact molten metal directly. Investment casting also involves wax-pattern tooling and ceramic shells. Select the board for the particular process stage in which it is used.

Unsaturated polyester board

Unsaturated polyester board suits shoe-mold masters, lasts and related models. Its useful hardness and ease of cutting, repair and sanding support shoe contours, edges and patterns at relatively low material cost.

The machined shoe-mold master is used to reproduce production molds in metal or other materials. If the board itself forms the footwear material, temperature, pressure and service life need separate assessment.

For ambient-temperature, short-run composite projects, unsaturated polyester board can provide an economical master, or a directly machined mold where the process permits. Direct molding requires assessment of resin contact, cure exotherm, vacuum sealing and repeated release, together with surface sealing. Heated high-temperature tooling requires the appropriate heat-resistant epoxy grade.

Unsaturated polyester board also suits color and appearance models. Noticeable machining odor is its main drawback. Where workshop ventilation is appropriate and the project can accept the odor, it is generally a lower-material-cost option.

Lightweight modeling board

Lightweight modeling boards are made from fine, uniform polyurethane foam. They are easy to CNC-machine and finish by hand for styling, color and appliance models, and automotive interior models such as seats and floors. Their low weight makes large bonded blanks easier to handle and modify.

9.36 lb/ft³ (0.15 g/cm³) suits early design models. Machining design data into a physical form allows rapid assessment of volume, proportions and surface flow, followed by cutting, sanding and repair. It can replace clay for some early design checks, but changes are mainly subtractive: unlike clay, it cannot be repeatedly heated, built up and reshaped.

12.49–21.85 lb/ft³ (0.20–0.35 g/cm³) suits appliance and automotive interior models. Appliance models usually support appearance and paint reviews; seat and floor models also check space and installation relationships. Select density according to thin edges, detail and handling. Dedicated supports should carry people or substantial connection loads.

28.09 lb/ft³ (0.45 g/cm³) suits more demanding exterior models. Higher density helps preserve detail and edges during fine machining and paint preparation. For prolonged, repeated component assembly or precise datum inspection, also compare PUBOARD modeling grades.

Lightweight board can be used for color models, with fine cells reducing sealing and priming work. Its hardness and indentation resistance are generally lower than conventional unsaturated polyester board. Protect thin edges, handling contact areas and fastenings; local connections can use high-density material or metal inserts.

06 Select adhesives together with the board

Large models usually require bonded blanks. The joints become part of the machined surface, so adhesive color, hardness, shrinkage and cutting behavior should match the board as closely as possible.

• Epoxy board: EPTEK offers compatible high-temperature epoxy adhesives. Bondline heat resistance and post-cure conditions should match the board and tooling cycle.
• Polyurethane board: select an adhesive suited to board density, with similar color, hardness and machining behavior, to reduce tool marks and sanding differences at joints.
• Lightweight board and foam: one- or two-component foam adhesives are options. Moisture-curing one-component adhesives require suitable cure conditions in thick or enclosed joints; two-component products require controlled proportioning and mixing. Hold the blank securely when using expanding adhesive to prevent expansion opening the joint.

Machine bonded blanks after the adhesive has fully cured, and check finished joints for pores and sealing. In prepreg tooling, adhesives, sealers and release systems also contact the resin and should be assessed together for cure compatibility.