Understanding the C Frame Double Crank Press – Types and Operating Principles

To meet the diverse technological requirements of different stamped parts, various types of crank presses are used in production. Each type has its own unique structure and functions. Crank presses are generally classified based on their functional characteristics and structural configurations.

1. Classification by Crank Press Function

Based on function, presses are divided into two major categories: general presses and common (special-purpose) presses.

• General Press: Offers versatile applications, including blanking, bending, forming, and shallow drawing.

• Common Press: Designed for a single, dedicated purpose, such as drawing presses, plate bending machines, plate shearing machines, automatic cold heading machines, high-speed presses, fine blanking presses, and hot die forging presses.

2. Classification by Physical Structure

According to physical structure, crank presses are divided into open-type presses and closed-type presses.

(1) Open-Type Press (C Frame)

Due to its "C" shaped body, the open-type press is also known as the C frame double crank press. It is open at the front, left, and right sides to facilitate easy installation and adjustment of molds.

However, the rigidity of the C frame double crank press is relatively low, making it prone to deformation under load, which can affect part accuracy and mold service life. Therefore, this design is only suitable for small and medium-sized presses. Based on body structure, it can be further divided into:

• Double-Column Open Press: The rear of the frame has an opening, forming two side columns at the upper part (hence "double column"). The cranks are supported on both columns, parallel to the front of the worktable. The body can also be tilted along the bottom frame (tilting press) to allow stamped parts to slide down automatically by gravity along the inclined rear opening, facilitating mechanization and automation.

• Single-Column Open Press: The frame has a hollow structure with only one column at the upper part (hence "single column"). The rear of the frame is closed, and operation is limited to transverse feed. A single-column fixed table structure is typically used for larger nominal pressure open presses. A single-column drop table structure allows adjustment of the press closing height over a wide range, making it suitable for diverse applications.

Based on worktable structure, presses are classified as fixed bench press or descending bench press. Based on body tilt capability, they are classified as tilting press or non-tilting press.

(2) Closed-Type Press

The closed-type press features a frame structure that is open at the front and rear but closed on both sides. Operators can only approach the worktable from the front or rear. The strength and rigidity of the closed-type press body are excellent, resulting in minimal elastic deformation under load and reduced impact on workpiece precision and mold operation. Therefore, closed-type presses are mostly large and medium-sized.

3. Classification by Number of Connecting Rods (Mechanism)

Based on the number of connecting rods, crank presses are divided into single-point, double-point, and multi-point presses.

• Single-Point Press: The slide is driven by one connecting rod; typically a small press.

• Double-Point Press: The slide is driven by two connecting rods; generally a medium press.

• Multi-Point Press: The slide is driven by more than two connecting rods (e.g., a four-point press uses two pairs of connecting rods). This ensures smooth slide movement, a large bed and worktable area, and good strength and rigidity, making it suitable for large presses. With two or two pairs of links, the slide is less sensitive to off-center loads.

4. Classification by Press Slide Action

According to press slide action, crank presses are divided into single-action, double-action, and triple-action presses.

• Single-Action Press: Features one slide mechanism; suitable for blanking, bending, and drawing of small to medium-sized parts.

• Double-Action Press: Has inner and outer slides. The outer slide holds down the material, while the inner slide performs deep drawing; suitable for large-scale deep drawing.

• Triple-Action Press: In addition to the inner and outer slides, a third slide completes an operation in the opposite direction of the deep drawing.

5. Classification by Location of Transmission Mechanism

Based on the location of the transmission mechanism, presses with the mechanism above the worktable are called upper drive presses, while those with the mechanism below the worktable are called lower drive presses.

6. Classification by Press Worktable Characteristics

Based on worktable characteristics, crank presses are divided into fixed table press, inclinable table press, descending table press, movable table press, rotary table press, and others.

7. Classification by Crank Type

According to the crank form, crank presses can be divided into crank press, eccentric gear press (fair press), crank and connecting rod press, and eccentric gear crank press (fair gear press).