3D Printing in orthopedic footwear technology

Shoe lasts milled from wood or molded and foamed

Traditionally, the last is milled from wood, preferably beech wood. The measurements of the outline of the sole, ball, instep, heel and calf circumference are taken, and the wooden block is then milled and sanded down after hours of precision work. Alternatively, plaster casts of the foot are filled with dual-component foam, which after hardening is finely sanded down. These processes are highly time-consuming and material-intensive – and correspondingly expensive.

Ordering molding blanks and sanding them to shape

The industry is helping orthopedic shoemakers save time by offering last blanks that generally already have the appropriate shoe size and the correct foot shape. Yet, especially in the field of orthopedic shoe technology, an enormous amount of reworking and fine-tuning is needed here as well until the last fits the customer's foot perfectly.

Configuring and milling CAD lasts

Those who have CAD software and the corresponding know-how can design individual lasts for their customers’ made-to-measure shoes themselves and either produce the finished models with their own milling machine or commission an external service provider to carry out this step. The latter, however, usually takes several weeks.

Accelerated last production using 3D printing

Whichever one of these approaches a specialized orthopedic shoemaker chooses, customized last production usually requires a few weeks of lead time before custom manufacture of the individual footwear can begin. This massive lead time can be significantly reduced if the shoe lasts are created using additive manufacturing . Apart from orthopedic shoe technology, this method also provides numerous benefits for classic made-to-measure shoe production or for prototype construction in series production of shoe lasts.

TPU as a material for 3D-printed shoe lasts

Conventional last manufacturing places high demands on the wood-based material used, as the material must withstand the heavy stresses it is subjected to in the shoe technician's workshop. Thermoplastic polyurethane (TPU) has proven to be ideal for PROTIQ in the additive manufacturing of orthopedic shoe lasts. This is a synthetic plastic that advantageously combines the elastic properties of rubber with high resistance to mechanical stress. The process parameters of the TPU were adapted in close cooperation with the material manufacturer BASF so that they optimally satisfy the requirements of orthopedic shoe technology. PROTIQ uses selective laser sintering (SLS ), a 3D printing process, to fuse the material layer by layer. This process allows for significantly higher precision and robustness than can be achieved by, for example, fused deposition modeling (FDM).

3D models of the lasts via CAD or 3D scan

To prepare the groundwork for additive manufacturing, footwear technicians can manually collect all relevant measurements of the foot and construct a 3D printed model of the individual last using CAD software. Those without the necessary program or capability can also commission an external provider to create a 3D print file based on the foot data. A time-saving alternative is to generate the data using a 3D scan . Orthopedic shoemakers equipped with an appropriate scanner (e.g., a mobile foot scanner) use it to record either a footprint or directly the foot of their customer. This provides digital data very quickly, which can then be individually processed on the computer.

Orthopedic shoe lasts from the 3D printer

Both methods incorporate the expert diagnostics of the shoe technician and the therapeutic goal for the affected or malformed foot directly into the last model. In the case of additive manufacturing, you can rely on the last coming out of the 3D printer exactly as it was modeled on the computer. This method is also suitable for producing particularly large-format lasts: Working with TPU manufacturer BASF, PROTIQ has qualified an appropriately sized 3D printing system specifically for this application. With the finished 3D-printed last, pre-qualifications can be carried out in no time at all using the company's own vacuum thermoformer, which is much faster and cheaper than printing a test shoe. All in all, this is currently the most innovative process in manufacturing individual customized shoes. Clients benefit from orthopedic footwear perfectly tailored to the size and shape of their feet, and which they can receive for fitting very quickly.

Advantages of TPU material for orthopedic shoe lasts:

• Excellent mechanical properties
• Virtually wear-free
• Withstands stresses from gluing, grinding and drilling without problems
• Pliability facilitates the removal of the lasts from the finished shoe
• Reduced weight of lasts in comparison with conventional wooden models
• Easy-grip surface improves handling

Benefits of additive manufacturing for orthopedic footwear:

• Very short production times
• High fitting accuracy thanks to computer-accurate last models
• Simple fitting options
• Reproducible last models that can be reprinted at any time
• All standard last pitches can be realized as required (2-part, 3-part, stair- or step-shaped and much more)
• Individual marking options for identifying the lasts

3D-printed shoe lasts in the workshop

The printed TPU lasts can be worked just as their wooden counterparts. The easy-grip surface guarantees a good and safe hold at all times and the low weight relieves the arms of the shoemaker. Nevertheless the lasts can withstand all of the typical working steps: They can be tacked or grinded wirhout showing any signs of abrasion. Even under high pressure or when milled or drilled they keep their original shape. 3D-printed shoe lasts are therefore in no way inferior to traditional lasts, in many ways even superior to them.