A definitive guide: Punch and Die

Tableting tools i.e., Punches and dies are essential tools to shape any granules into a solid dosage form by applying compaction force in a compression machine. Any shape be it round, capsule, animal shape, bullet shape or any special shape can be obtained with the help of the standard tooling. In the case of making solid oral dosage form like tablets, tableting tools like upper punch, lower punch, and die are important. They help to shape lubricated blend (called granules) into a solid form by using a compression machine that applies pressure. These tools can create different shapes like round, capsule, oval, animal-shaped, bullet-shaped, or other special shapes.

Upper Punch:

Lower Punch:

Die:

Basic Tablet Tooling Terminology:
i. Head: The head which rests on the cam, moves on the cam during a compression.

ii. Head Flat: Head flatness is vital, and its size varies depending on tooling types. Compression rollers in a compression machine press this head flat and that’s where actual compaction takes place.

iii. Head Chamfer: A head chamfer is provided to remove the sharp edges for smooth operation in the cam.

iv. Head Degree: Head degree facilitates smooth movement in cam.

v. Neck: It acts as a supporting part for the head and body for fitment and allows easy movement in the punch bore.

vi. Neck to Head Radius: This radius helps tools for easy fitment and avoids any sharp corners that can wear out the turret surface.

vii. Neck to Barrel Radius: This radius assists tools for easy fitment and avoids any sharp corners that can wear out the turret bore.

viii. Barrel Chamfer: It facilitates avoiding any damage to the turret bore.

ix. Tip Undercut: Tip undercut acts as a scraper blade for the die bore to remove the sticky granules.

x. Tip Radius: Tip radius offers strength to the tip during compression as the tip needs to travel to a particular length in a Die bore.

xi. Barrel or Body: This part of the tool is used for fitment and sliding in the punch bore.

xii. Key: The key is used mostly in the upper punch for aligning the upper punch tip concerning the die and avoids any kind of rotation during compression to prevent major accidents.

xiii. Groove: The grooves are designed such that a dust cup can be fitted to avoid the contamination of any foreign particles coming from the upper punch turret bore.

xiv. Tip Length: Tep length defines the penetration point of the tip inside the die bore.

xv. Tip: Tips is your actual tablet size and its cavity provides shape to the tablet during compression.

xvi. Cavity: Cavity is the area where the powder gets filled to form a shape during compression.

xvii. Die height: Die height is defined as per the die plate bore slot thickness.

xviii. Die O.D. (Outer diameter): Die OD is the die bore slot in die plate.

xix. Die Groove: This is the slot where the die lock screw is fixed.

xx. Die O.D. (Outer Die) chamfer: This chamfer reduces sharp edges which can wear and tear the die bore surface.

xxi. Die I.D. (Inner Die): This chamfer minimizes the damage to the die bore surface and easy movement of punches inside the dies.

xxii. Tooling Set: A single tooling set comprises of upper punch, lower punch and die. These punches move vertically in turret bores through cams and compress to form a tablet.

As per international standards, i.e. TSM (Tablet Specification Manual) and EU (Euro Standard), tooling specs have been standardized so that inventories worldwide can be minimized for tablet presses. All international manufacturers follow EU standards and TSM standards mostly followed in the United States of America and Japan.

xxiii. Upper punch: The upper punch is fitted in the turret bore and moves vertically in bores during compression. Upper punches make the upper cavity of the tablet. It is fitted with a key for alignment with the die bore in case of shape punches. For round punches, there is no need for a key in upper punches. Upper punches travel 5-6mm inside the die bore during compression and as per the penetration setting done in a compression machine. Tip Length is shorter in the upper punch compared to the lower punch. The tip length of the upper punch is generally 8 mm-9 mm.

xxiv. Lower punch: The lower punch is fitted in the turret bore and makes the lower cavity of the tablet during compression. The lower punch tip always stays inside the die bore hence there is no need for a key in case of lower punch. Tip length is relatively longer in the lower punch as it has to cover the entire height of the die and eject the tablet. The lower punch tip length is 25-28mm.

xxv. Die: Die is fitted in the die plate. Die bore in die is actually where the filling of powder is done. The upper punch tip and lower punch tip compress the powder in the die bore with the help of compression roller pressure applied on the head flat during compression to make the required shape of the tablet.

Tooling Types:
There are different types of tooling i.e. D, DB, B and BB types. Apart from these standard types, there are FS tooling, BBS tooling, A tooling and Chinese standard tools which are totally different from International standard tools.

Tooling recommended for tablet:
If the client has 27 station tablet press, then they will buy 30 sets or 35 sets of tooling keeping a few sets extra as spares but now only 27 sets can be used. There are various factors related while considering tooling type where the client relies on tooling manufacturers for their inputs. E.g., if a client wants to make a tablet of size 9mm, then what type of tooling should be considered? Now factors like product nature need to be considered whether granules are sticky, hard, fines in granules, or require high compression force. Generally, any client will choose the B or BB type of tooling which provides higher output as the number of tooling stations is more compared to the D type. Manufacturers offer quality alloy steels to overcome compression force requirements, but some tools require more dwell time (more contact time between head flat and compression roller) and high compaction force, in those cases, D tooling becomes an auto option in such cases. The head flat can be increased in B tooling as well but the strength and dwell time that D can offer, it’s not possible in B tooling. But in case the powder is non-sticky, good flowing nature and requires standard compression force then B or BB tooling is the best option as the output will be more in that case.

How to maintain Punches and Dies?
The maintenance of compression tooling becomes easy by following these mentioned steps:
Step 1: The punches and dies must be cleaned on a periodical basis. They can be washed in water and dried using a cloth.
Step 2: They must be evaluated with the proper and high-quality maintenance equipment before their installation as well as after using it for a certain time to increase their shelf life.
Step 3: The regular inspection of punches and dies will provide us with information if any punch or die is corroded and whether it requires any repairing or not. If it is required, a prompt step must be taken towards it to decrease its negative effects.
Step 4: Measuring tools with the help of equipment and polishing them whenever required will boost their performance by which accurate production will become possible.
Step 5: Lubricating compression tooling will decrease friction and enhance the operational activity of the tablet press machine. A range of non-toxic, FDA-approved oils and greases are recommended for different applications such as preservatives or lubrication purposes. One should also take a note to store them in a safe and moisture free place.

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