Chapter 1: Importance of Fixed seal master cylinder precision machining in automobile braking system

A decade ago, electric vehicles seemed like an unattainable aim and a fancy dream. In the last decade, the automobile industry has seen significant improvements in engine efficiency, speed, comfort, more versatile, aesthetic automobiles, and safe vehicles. Even with all of these improvements and innovations, the fundamental concern for automotive manufacturers and customers is the driver's and their family's safety.

When thinking about vehicle safety, the first thought is airbags. One of the essential parts of a vehicle is the braking system. People can avert serious highway accidents if the brakes are efficient. 

As a result of modernization and cutting-edge technology, we now have more secure and efficient braking systems. Even the most recent EVs employ the same braking mechanism as a traditional internal combustion engine. It provides alleviation and a platform for the maker of the braking system and braking parts.

In the previous article, We covered the manufacturing process of a tandem master cylinder using two alternative technologies and the benefits and cons for manufacturers. This series of articles will look at the manufacturing of fixed-seal master cylinders to better understand the real opportunity and manufacturing process.

Fixed Seal Master Cylinder is also known as a stationary seal master cylinder. We explained the tandem master cylinder braking application in our previous article. This article focuses on an advanced new piston and master cylinder design known as the fixed seal version. 

Please find below the cross-sectional assembly of the Fixed seal Master cylinder:

 A fixed seal master cylinder is designed for various vehicle braking systems to deliver hydraulic force to the car's braking mechanism. However, there is still a demand for more compact fixed seal master cylinders that can be manufactured at a cheaper cost.

Working principle and design characteristics of fixed-seal master cylinder:

The master cylinder, including the master cylinder housing, defines the primary bore in this enhanced fixed seal system, and the bore defines an elongated axis. The seal grooves in the master cylinder housing are accurately machined. The seal groove positions are controlled by precise groove diameters and depths, allowing the piston to glide tightly and accurately within the bore following the seal assembly. The piston's distal end and the chamber formed in the distal end were included. The chamber is designed to contact the seals as long as the piston clears the bypass holes.

Another design feature is an improved piston-to-seal configuration for the fixed seal master cylinder. The master cylinder housing defines a generally cylindrical bore, the bore defining the elongated axis, and the seal groove defining the master cylinder housing and opening generally circumferentially on the bore. 

The position of the seal groove within the seal groove, and the seal, which includes inner diameter lips extending radially inwards into the bore. The piston slides within the bore to define the piston fluid chamber and the forward fluid chamber, where the piston moves relative to the seals and has a chamfered distal end. The piston is free of bypass holes to form a seal between the piston, fluid chamber, and forward fluid chamber. It is designed to engage the seal's inner diameter lip.

The seal has an exterior diameter lip that fits into the seal groove. The master cylinder has an inner diameter lip radially inwardly based on the bore axis. The inner diameter lip is designed to engage the piston's chamber. The piston also has a sealing surface, and the inner diameter lip of the seal is designed to interact with the sealing surface when the piston is moved distally.

The piston defines the piston fluid chamber and a forward fluid chamber within the bore. The piston fluid chamber connects to the bore via a fluid flow route. The master cylinder in which the inner diameter lip of the seal is fitted to engage the chamber at the distal end of the piston to impede the fluid flow channel. The master cylinder has an inner diameter lip suited to produce a seal between the piston fluid chamber and the forward fluid chamber.

The master cylinder is filled with hydraulic fluid in the piston fluid chamber and forward fluid chamber, and the seal is made of an elastic material. The master cylinder housing has a typically cylindrical bore and a seal groove circumferentially distributed around the bore's inner diameter. The piston is linked to the master cylinder's principal circuit. It also includes a second piston that fits snugly and slidably within the bore and is connected to the master cylinder's secondary circuit.

The necessity of precise and efficient braking systems:

Because of the high speed of today's motor vehicles, the brake force necessary to stop or de-accelerate the vehicle efficiently is also significant. Mechanical braking cannot be correctly satisfied. Hydraulic braking with a fixed seal master cylinder is the new necessity of today's automobiles. A fixed seal master cylinder is very compact and generates more braking force.

Because the part is the mother of this vehicle's safety feature, the exact machining of seal grooves is critical during the manufacturing process of the fixed seal master cylinder. Only when the required accuracies are attained throughout the machining process can efficient braking occur. Within the acceptance limit, bore tolerances and geometrical accuracies are monitored.

Some suppliers supply complete brake assemblies, while others provide only machined master cylinders. Acceptance becomes complicated if the supply is limited only to the component machining. Suppose there are a few days between completing the machining and using the component for assembly. The machining is done with a water-based emulsion. In that case, the aluminum alloy components get a black surface mark on the bore dia due to natural oxidation. Using neat oil will aid in the prevention of the black spot on the inside bore.

Machine configuration considered for this process:

The machine used to demonstrate this method was configured as shown below.

Twin spindle twin pallet machine horizontal machining center.

Machine Configuration:

1. X-Axis travel 320mm, servo axis with rapid travel 60 m/min, with brake motor option.

2. Y-Axis travel 800mm, servo axis with rapid travel 70 m/min, with brake motor option.

3. Z Axis travel 400mm, servo axis with rapid travel 60 m/min, with brake motor option.

4. Center distance between two spindles 320 mm.

5. W Axis servo drive, with 64 tools capacity.

6. A1 Axis hydraulic with encoder for pallet positioning of rotary pallets.

7. A2 Axis servo with torque motor, 4th axis rotary axis.

8. A3 Axis servo with a torque motor,4th. And the 5th axis is the rotary axis.

9. Spindle1 & 2 with 22 KW power and 126 nm torque,12000 rpm, with through coolant and high-pressure options for 60 bar.

10. Hydraulic counterbalancing.

11. CNC system Fanuc 31iB or Siemens 840D

The machine has considerable flexibility to finish the machining process while reducing total cycle time, according to the parameters above, with high quick travel for all three axes. In this situation, the travel time for tool change within the component will be short; both face to face and hole to hole, thus saving idle time.

The machine exhibits a direct tool change, which occurs with simultaneous movement of the X, Y, and Z axes, resulting in a tool change time of 3 to 5 seconds.

Furthermore, the chip-to-chip time will be 5 seconds.

The pallets A2 and A3 are rotating axes with servo torque motors, and the rotary drums each have a 500-diameter working envelope. The A2 axis is a servo fourth axis, and the A3 axis is a servo fifth axis. According to the method, the part can be oriented to any angular position.

Two spindles with high power and torque on the spindle housing can support heavy metal cutting. With a coolant pressure of 60 bar, these spindles are coolant through feasible. These machines performed admirably on aluminum alloy components during roughing, finishing, milling, drilling, rough boring, and finish boring operations.

Two clamping settings are required for the fixed seal master cylinder. One with the fourth axis for four component loading, the cylinder bore, flange face milling, front face grooving, and primary and secondary inlet holes, and these operations are scheduled on the first setup. Another arrangement with the 4th and 5th rotational axes is planned for the A3 pallet.

The machines support two-channel ideas, such as loading/unloading and machining stations. During the machining process, the chips land in the bed rather than on the fixture plate. The bed flushing constantly operates at 4 bar pressure to move all chips to the chip conveyor.

The tool magazine is designed to contain eight tools, one for each drum segment's intended length. Some segments can carry more data. Some parts can accommodate longer tool lengths of up to 320 mm. The shortest tool length is 160mm.

The tool's maximum length and maximum diameter can be designed based on the constraints and needs of the machining and operations. Suppose a larger diameter tool is required for the process. In that case, the neighboring tool pocket can be left vacant or put a smaller diameter and shorter gauge length tool in the magazine.

With correct tool mapping in the magazine and segment rows, we can plan and organize the tools according to the running process, reducing idle time for tool change movement.

This article summarizes the fixes-seal master cylinder and the machining procedure required. This article taught us about the necessary machine configurations and their capabilities. The following article in the same series will thoroughly inform the machining process, including all the required machining data, such as machine use, cutting speed, tool parameters, and precautions.

Click here for Chapter 2 >>>>

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