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As for size, any tip 4 millimeters or less in diameter is at risk of distortion or breakage and preventing that can be quite a design challenge. One solution is to reinforce the punch tips, as shown in Figure 1. In this case, the small- diameter tips required equipping the press with a restricted fill cam, which limits the movement of the lower punch and restricts the depth of fill. That prevents the punch tips from dropping too low in the die bore. This design also includes recessed dies to accommodate the reinforced tips and to prevent them from contacting the die bore. As with single-tip tooling, the tablet profile, emboss- ing, and break-line details are critical design elements. Seek the expertise of a professional tooling designer to account for these and the many other variables that come into play when developing a multi-tip configuration. Most tablet designs are compatible, but the type of press and the type of multi-tip tooling must be considered. Types of multi-tip punches There are four main types of multi-tip punches: inter- nal cap fixing, external cap fixing, pin fixing, and monoblock (Figure 2). The cap and pin fixing designs, all of which combine several components, have been around for many years. Monoblock multi-tip punches—so named because they are made from a single piece of steel—are the most recent type and became available because of advances in CNC machining. Each type has benefits and drawbacks. Internal cap fixing. This design offers a clean method of fixing the tips, which are easy to replace if damaged. Its seamless joints don't interfere with the punch guides or oil/dust seals, minimizing contamination. The internal cap is secured with self-locking screws that prevent it from coming loose. Because the design comprises several compo- nents, it's easy to combine different materials and coatings. External cap fixing. This design resembles internal cap fixing, but because the cap is fitted to the outside of the punch body, more space is available and it can accommo- date more tips per punch. Pin fixing. If the application calls for punch tips that are easy to replace, pin fixing is the best choice because it is a simpler design with fewer components. Monoblock. This design requires no disassembly before cleaning or reassembly thereafter and is preferred for WIP and other applications that require the tooling to be easy to clean while it is mounted on the press. Because it has no joints, the monoblock design will not damage the punch guides or seals. It also reduces the risk of cross- contamination. The one drawback of monoblocks: A damaged tip requires replacing the entire punch. 32 March 2015 Tablets & Capsules Figure 1 Reinforced small-diameter tip with recessed die to prevent it from contacting the bore Figure 2 The main types of multi-tip punches Internal cap fixing Monoblock External cap fixing Pin fixing Fixing screws Individual tips Individual tips Fixing pin Fixing pins Individual tips Punch body Punch body Cap Cap To ensure your multi-tip tooling remains in good working order, follow this standard operating procedure. 1. Clean. It's essential to remove all contamination. The easiest multi-tip tooling to clean is the monoblock. 2. Assess. Inspect the punches and dies to determine their general condition. 3. Repair. Rectify any damage to the tooling, including any light corrosion and/or minor damage by manual polishing. Only make repairs when absolutely necessary. 4. Measure. Ensure the tooling's critical dimensions are within tolerance. For multi-tips, focus on measuring the working lengths of each tip on the punch and the working lengths of the punches across the set. Keeping them within tolerance will help you control tablet weight, hardness, and thickness. 5. Polish. Use an automated polisher to ensure a consistent, uniform finish. 6. Lubricate. Apply a light oil to the tooling to protect and preserve it and to help ensure the tablet press operates smoothly. 7. Store. Eliminate or minimize damage by using dedicated storage cabinets. Keep accurate records about the tooling. —S.O. and S.D. Tooling maintenance in seven steps