Die Cutting

Chapter 1: What is Die Cutting?

Die cutting is the mass fabrication of cut-out shapes by shearing a stock material such as paper and chipboard using tooling called a die. A die is a specialized tool used in manufacturing to cut or shape a material fitted into a press. It has sharp edges used to pierce the material; it contains the custom two-dimensional shape of the finished part. The die cutting process works in the same principle as the cookie cutter where the dough is cut into smaller sizes. Examples of materials which can be die cut are paper, fabric, rubber, fiberglass, metal sheets, and plastic.

Die cutting started in the mid-19th century to modernize the shoemaking industry. Before die cutting was invented, manual labor was utilized to outline and cut the soles of the shoes by hands. This process required more time and manpower while the rate of production was low. The invention of die cutting resolved these problems in the industry. Patterns were made allowing shoemakers to replicate and standardize the sizes of the soles. Through years of discovery, die cutting had extended to revolutionize other industries and it is still evolving to cater to increasing demand and in making more complex designs. Today, this method is widely used in the manufacturing sector such as packaging, consumer goods, and automotive industries. Applications of die cutting can even be found in our homes and offices.

Since it is a simple and straightforward process, die cutting is suitable for low or high volume manufacturing. In industrial applications, the machine may be located directly downstream, while the starting material may be the outgoing product from a preceding process. The die cutting machine also has many capabilities, making it a versatile and useful asset. It can perform other operations aside from cutting, such as forming, perforating, and scoring. The process is done on a press through a single or series of strokes.

Flatbed, rotary, and semi-rotary die cutters are considered industrial-scale die cutting machines, designed for thicker and more rigid substrates able to produce parts at a fast turn around. Meanwhile, manual and digital die cutting equipment are utilized to create simple and accessory parts. Its production rate is relatively slower and therefore suitable for low volume orders.

Chapter 2: Flatbed Die Cutting

Flatbed die cutting is also known as steel rule die cutting. A flatbed die cutting machine uses a hydraulic press or a mechanical or electrical system to press down the custom-designed steel rule die to the material. This method is suitable for cutting thicker sheets (over 1/8”) as it is capable of exerting high pressures. A variety of materials can be processed using a flatbed die cutter, ranging from soft to semi-rigid materials with varying thickness.

Flatbed die cutters can operate in batch or semi-batch (wherein products are collected periodically) production and are suitable for processing small production orders and larger parts. This machinery involves the following sub-processes to produce the finished part from the substrate sheet:

• Feeding

  The stock material is transferred from the feed tray, or a roll, to the flatbed through a suctioning, pushing, or pulling system. In this section, it is important to control the feed rate and positioning of the sheet to achieve a precise cut and prevent cutting errors.

• Cutting

  The cutting assembly is composed of a die board and a lower counter plate. The die board is the flat and rigid upper plate which contains a series of knives used to cut the stock material into finished parts. It is designed to be shock-absorbent and warp-resistant to withstand high pressures, to produce a precise cut, and prevent the material from deformation. Customized tools are attached to the die board to define the form of the finished part.

  • Steel rule

    The steel rule, or the cutting edge, is a piece of metal bent to form the outline of the finished part. The pressing of the steel rule unto the material may induce full cutting or partial cutting.In full cutting, the cut extends to the entire thickness of the material, extending to all layers. This process causes the part, an enclosed area, or the hole to be separated from its remainder. Partial cutting is done through the use of a lower rule blade. The lower rule blade is slightly narrower than what is used in full cutting so that it only cuts a portion of the material’s thickness. The lower rule may not be sharp to create folds.

  • Punches

    Punches are inserted on the upper plate to form internal cut-outs which come in standard shapes (circle, oval or square) and sizes. Punches that are the self-ejecting type usually have a larger diameter than the holes they created.

  • Rubber ejection strip

    These strips are self-adhesive rubber placed around the rule to remove the finished part after cutting.

  To complete the cutting assembly, a lower counter plate is placed wherein the stock material is mounted and supported during the cutting process. The cutting head initiates a downward stroke to apply pressure perpendicular to the plane of the material’s surface. This pressure compresses the material, causing the edges of the die to penetrate against it. The die board comes in different configurations, depending on the cutting and punching steps involved:

  • Simple Die

    In a single stroke of the press, the simple die performs only one cutting.

  • Compound Die

    In a single stroke of the press, the compound die creates more than one cut or impression on the web. A typical example of this die type is found in the production of a washer. With this type of die, cutting the outline and piercing of the inner hole is done in a single stroke.

    

    
    

  • Progressive Die

    A progressive die is used when there are a series of cutting and secondary steps involved to create a finished product. Each stroke creates a different cut or impression, and in between strokes, the sheet is transferred to the next operation. This process requires precise set-up and alignment of the stock material. The part remains in the stock material until it comes to the last station where it is fully separated. The more operation the die performs, the more complex design the die must have; also, the more difficult to optimize the pressure to be used.

    

    
    

  • Combination Die

    A combination die performs multiple cutting and forming operations (such as extruding and bending) using a single stroke.

    

    
    

  To achieve a good cut, the properties of the material to be processed must be considered. Thicker and more rigid materials must require thicker dies and higher pressure.

• Stripping

  In this step, a single finished part is separated from the excess material and other parts produced in the batch, either manually or by mechanical means. The excess material may be reprocessed or recycled.

Chapter 3: Rotary Die and Semi-rotary Die Cutting

Rotary die cutting machines operate in continuous production mode. It operates at a lower cutting pressure and constant speed, which is ideal to be located directly downstream of a preceding process. Hence, rotary die cutting machines are used to produce simpler and lighter parts. It is suitable for a variety of materials and gives a faster turnaround time than a flatbed die cutter.

The stock material, or referred to as web, in the form of an individual sheet or roll, passes through the cutting assembly. The cutting assembly is composed of a rotating cylindrical die affixed to a rotary press and an anvil cylinder pressed against the rotary press. The two cylinders are continuously rotating in opposite directions along the horizontal axis. As the web passes through the two cylinders, it is compressed until the sharp edges of the die pierce through the material’s thickness.

A rotary die cutting machine is also capable of full and partial cutting. However, it is not capable of punching holes. Like flatbed cutting machines, the steps are the same but differ on the mechanism of the cutting assembly.

There are two types of rotary dies, depending on the properties of the material to be cut and economics.

• Flexible Rotary Die

  Flexible rotary dies are made of thin sheets of steel with engraved patterns, which contain the edges for cutting, wrapped around a base magnetic cylinder. These dies are suitable for low pressure and shallow or partial cutting. The cutting thin sheet can be replaced depending on the part to be cut. The magnetic cylinder can be configured for many flexible dies.

  These types of dies are easily manufactured and less expensive. It also requires less downtime during replacement. However, these are less durable than solid dies.

  

  
  

• Solid Die

  A solid die has engraved, abrasive patterns on the rotating cylinder itself. This type is intended for higher pressure applications than the flexible die. The solid engravings can exert higher forces that enable the die to create deeper cuts on thicker and multi-layered materials. The solid die can be sharpened once worn-out. This type of die is more durable and flexible. However, it is more costly in terms of initial and maintenance costs.

  

  
  

When operating a rotary die cutting machine, the following operating and material conditions are considered:

• The tangential speed of the rotating cylinders and the speed of the web must be the same. This ensures proper placement of the material between the two cylinders, resulting in precise and uniform cuts through the entire length.

• The clearance between the rotary press and anvil cylinder must be optimized according to the thickness and compressibility of the stock material. If the clearance is too narrow, higher cutting pressure will be applied which may cause fatigue in the machine components. On the other hand, if the clearance is too large, the cutting pressure is not sufficient to cut the sheet properly. Large clearances are suitable only for partial cutting.

• The rotary die to be selected must have a blade width and angle that is optimal for the material to be processed. Thicker and more rigid materials require a wider and steeper blade.

Semi-rotary Die Cutting

This type of die cutting machine is almost similar to a fully rotary die cutter, except that it only uses one cylinder, which contains the die, for cutting. The semi-rotary die cutting equipment is programmed such that the cylinder moves in a single direction while the web moves back and forth. The movement of both cylinder and web creates multiple cuts, eliminating the need for another cylinder.

Semi-rotary die cutting machines are less expensive than fully rotary and flatbed die cutters. However, it is only limited to low-pressure applications.

So far, industrial-scale die cutting machines have been discussed. The following equipment creates simpler parts with relatively low production rate, hence considered as small-scale:

• Manual Die Cutter

  Manual die cutters work by pushing the crank lever which forces the steel dies to the substrate, hence cutting out the finished part. Soft materials like paper are best for this type.

  Manual die cutting is suitable for cutting out auxiliary items. This equipment is small and portable, typically found in homes, offices, and craft tables.

  

  
  

• Digital Die Cutter

  A digital die cutter is a versatile cutting machine which is controlled by computer software or cartridges. Unlike the traditional die cutters, it does not have steel dies but is equipped with sharp blades inside the equipment. This equipment is powered by electricity. Like the manual die cutter, digital die cutting machines can be installed indoors.

Chapter 4: Capabilities of a Die Cutting Machine

The die can be customized to add details and auxiliary purpose to the finished part, depending on the end application. The capabilities of a die cutting machine are:

Through Cutting

Through cutting is a type of die cut in which the sharp edge of the die extends through the material’s entire thickness, resulting in full separation of the part. For multi-layered materials, the face, adhesive, and backing material layer are cut through.

Kiss Cutting

Kiss cutting, on the other hand, is a type of cut in which the edge of the die partially cuts through the material’s thickness and only forms the perimeter of the finished part. For multi-layered materials, only the face and adhesive layer are cut. The part is not fully separated from the stock material but can be easily detached on the kiss cut.

Perforating

Perforating, or sometimes called piercing or coining, is a type of die cut which leaves a series of small, punched holes placed collinearly in the material by using a pressurized force on the finished part. The spacing of the holes determines the ease of cutting the material. The perforated lines will not result in the separation of the part from the stock material, but it can easily detach along the line.

Cut Scoring

In cut scoring, the die leaves a partial cut or a small indent at a single stress point aligned collinearly on the material rather than cutting its thickness entirely. The die only cuts less than half of the material’s depth, piercing it to make tearing easy.

Crease Scoring

Creasing also creates indents aligned collinearly by applying pressure to reduce the material’s thickness on one or both sides of the material. The die does not create a pierced or cut perimeter, and the depth is not extensive as a cut score. The crease score makes even folds to aid in creating a three-dimensional profile out of the material. The folds created from this process are more flexible and precise.

Broaching

Broaching uses dies with a combination of multiple teeth that pierces together on a single stroke to cut extremely thick or rigid material. Other die cutting machine capabilities utilized to decorate the finished part are embossing, engraving, forming, and drawing.

Chapter 5: Design Considerations for Die Cutting Process

The design of the part and its details, together with its material properties, have an impact on the manufacturing process and the outcome of the finished part. Poor design can lead to losses during processing and handling of the finished part, as well as inconvenience to the end-user.

The following are the four basic elements of die cut parts and the minimum guidelines when designing. All of these primarily consider maximum reliability during handling and service life.

• Blanks

  Blanks are the cuts that form the edges of the finished part. It separates the part from the stock material during the stripping stage. Sharp internal or external corners must be avoided during the part and die design, as this serves as a stress point during stripping and handling. At this stress point tearing and fracture commonly occurs, especially for thin and soft materials.

  

  
  

  Rounded internal or external corners prevents tearing and fracture, resulting in a more durable and long-lasting part.

• Holes

  Holes are empty spaces that are enclosed within the perimeter of the part. It can be made by using a punch or by the steel rule itself. However, its placement along the plane is limited to prevent tearing and inconvenience:

  

  
  

  • Place the hole at least twice the material thickness from the edge to prevent tearing and bulging during the stripping step and handling process.

  • If a series of holes or other similar design features must be made, the clearance between two adjacent holes must be twice the material thickness. If possible, a single oblong hole may be considered to replace the series of holes.

• Scores

  Scores in the form of cuts, creases, and perforated scores make folding and tearing convenient for the user. However, it gives additional stress points in the finished part.

  • Place a series of holes four times the material thickness away from the score line.

  • Avoid placing a hole in the score line. This prevents unwanted tears.

• Tabs

  Tabs are included in the part design to attach corners and edges. This attachment gives the stock material its three-dimensional feature. A tab may be located outside the edge (external tab) or enclosed within the plane (internal tab).

  

  
  

  • If holes are to be made in the tab, place the hole at least twice the material thickness from the edge.

  • Place a hole to terminate the internal ends of the tab. This is to dissipate the stress which causes cracking or tearing during handling. The internal ends should not be terminated with a bare end.

Conclusion:

• Die cutting is the process of cutting a sheet or roll of stock material into a smaller and more useful form using tooling called a die. It dates back to the mid-19th century to modernize the shoemaking industry. This manufacturing process has evolved to meet increasing demand and create more complex designs.

• The stages of a die cutting process are feeding, cutting, and stripping, which is common to all die cutting methods.

• Flatbed die cutting machines utilize an assembly to cut the stock material through a press. These machines are capable of operating at high pressures, giving a more precise and deeper cut.

• The press of a flatbed die cutting machine consists of a die board and a lower plate. The die board contains the cutting and punching tools, and a rubber ejection strip. The lower plate supports the stock material during cutting.

• The die board has several configurations depending on the cutting steps involved: simple, compound, progressive and combination dies.

• Rotary die cutting machines operate in continuous production mode at a constant speed and lower pressures. It utilizes two cylinders: a cylindrical die and an anvil rotating in opposite directions to cut the moving web.

• The two types of rotary dies are flexible die and solid die.

• Die cutting machines are also capable of making kiss cuts, scores, and perforated holes, which define the characteristics of the part.

• There are part design considerations for the die cutting process to maximize reliability during handling. The four basic elements of die cut parts (blanks, scores, holes, and tabs) are considered.