Chapter 1: Importance of Tandem Master Cylinder precision machining in automobile braking system

Importance of Tandem Master Cylinder precision machining in the automobile braking system, chapter 1

Technology and modern machinery always bring convenience, dependability, and a sense of progress. However, this is not always the case. One such technology can sometimes cause more concerns for the manufacturing industry than it solves, particularly in the automobile industry. Any advancement or new technology in any vehicle must address the most pressing concern: IS IT SAFE FOR THE DRIVER AND PASSENGERS?

No matter how far or advanced the capabilities of the new invention bring to the vehicle, if it raises even a minor safety concern, it will be avoided and should be avoided by the industry.

When we think of safety, the first thing that comes to mind is a vehicle's braking system. Unsurprisingly, we see many failures of braking systems in movies. Not because it is a cool or well-known movie trick, but it is one of the most uncommon, yet terrifying and dangerous, causes of accidents. As per the Indian Roads & Transport Department report, nearly 1.5 lakh people die in road accidents in India every year. India accounts for nearly 11% of all accident-related deaths worldwide. It is why manufacturing automotive braking systems has become a priority. Any flaw in a component of the braking system can endanger the entire system's operation.

The Tandem Master Cylinder is one of the manufacturers' most common parts of this braking system. This article will cover the detailed manufacturing process of Tandem Master Cylinders with the highest precision possible. This process overview will include a complete setup, desired operations, tools used, and machinery information.

What is the function of the Tandem Master Cylinder?

The master cylinder converts the pressure applied by the driver's foot into hydraulic pressure, amplified by the brake booster. This pressure is converted by the master cylinder, which controls the process by feeding hydraulic oil into the braking circuit. It can be called the heart of the car's brake system.

Tandem master cylinders consist of primary and secondary pistons within the same cylinder bore. It generates hydraulic pressure for two separate brake circuits; if one brake fails, braking pressure builds up in the other circuit, allowing the vehicle to be controlled. Due to the obligations of safety standards, this has become a statutory requirement in many countries.

When the driver pushes the brake pedal;

• A pushrod drives the primary piston, compressing the circuit's brake fluid.
• Hydraulic pressure builds inside the cylinder and brake lines as the primary piston moves.
• This pressure causes the second piston in the circuit to compress the brake fluid.
• The braking mechanism is activated when brake fluid flows through the brake lines.

When one lets go of the brake pedal, the springs return each piston to its starting position. It relieves system pressure and disengages the brakes.

The advantages of automobile tandem master cylinder brake systems include increased vehicle safety by activating the brakes using vacuum pressure if the brake fluid is lost. The tandem master cylinder has two pistons in one bore, and when the brake pedal is pressed, the piston exerts pressure on the compression spring attached to the rear of the secondary piston. This process is based on the theory of Pascal's law, which states that high-pressure fluid is obtained at the outlet of a smaller cylinder area by applying force to the larger area of the inlet. The two distinct hydraulic chambers produce the effect of two distinct hydraulic braking circuits. If one circuit fails, the other circuit can still function and cause the vehicle to stop. Although, the braking distance will be longer in this case. Abruptly applying the brakes will not help.

Because of the high speed of today's automobile vehicles, the brake force required to stop or de-accelerate the vehicle efficiently is also high. Because mechanical braking is ineffective, hydraulic braking with the master cylinder is the new requirement of today's vehicles since it generates more braking force.

Because the master cylinder is the mother of this vehicle's safety feature, precise machining is essential during manufacturing. When the required accuracies are achieved during the machining process, efficient braking can occur. Within the acceptance limit, bore tolerances and geometrical accuracies are controlled.

Some suppliers supply complete brake assemblies, while others supply only machined master cylinders. Suppose the supply is limited only to the component machining; then, acceptance becomes complicated because there is a lag of a few days between the completion of the machining and the use of the component for assembly. If the machining is done with a water-based emulsion, these components get a black surface mark on the bore dia due to the natural oxidation of the aluminum alloy. The neat oil will aid in the prevention of the black mark on the internal bore.

Desired Machine configuration considered for this process:

The machine used to prove this process was as per the below configuration.

Machine Type: Twin spindle twin pallet 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. The Center distance between two spindles is 320 mm.
5. W Axis servo drive, with 64 tools capacity.
6. A1 Axis is hydraulic with an encoder for pallet positioning of rotary pallets.
7. A2 Axis servo with torque motor, 4th axis rotary axis.
8. A3 Axis servo with torque motor,4th axis 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 enough flexibility to complete the machining process while reducing overall cycle time, according to the specifications above, with high rapid travel for all three axes. In this case, the travel time for tool change within the component will be short, both face to face and hole to hole, ultimately reducing 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 rotary axes with servo torque motors, and the rotary drums each have a 500-diameter working envelope. A2 and A3 are the fourth axes of servos. According to the process, 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. These spindles are cooled through feasibility with a coolant pressure of 60 bar. These machines performed admirably on aluminum alloy components during roughing, finishing, milling, drilling, rough boring, and finish boring operations.

Three clamping setups are required for the tandem 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 planned on the first setup. The other two setups are planned for the A3 pallet's top and bottom faces.

The machines are designed to support two-channel concepts, such as machining and loading/unloading. The operational zone which generates the chips falls directly into the machine bed. The bed flushing runs continuously at 4 bar pressure to transport all chips to the chip conveyor.

The tool magazine is designed to hold eight tools, one for each drum segment's intended length. Some segments 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 limitations and requirements of the machining and operations. If a larger diameter tool is required for the process, the adjacent tool pocket can be left empty, or smaller diameter and shorter gauge length tool can be mapped in the magazine.

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

Fixture Concept 

In some cases, the fixture must be designed to accommodate more than one component; in these cases, the fixture setup must be managed using interchangeable parts or a separate setup. We can use the top face of the pallet for one component and the bottom face for another.

Component Image

Component datum component 1

Component Resting: Q1Q2 and Q3Q4 at two separate "V" Block 

Component Orientation: Q5 and Q8 (Intersection Point Q6/Q7)

Component Clamping: Against Resting

Component datum component 2

Component Resting: Q1Q2 and Q3Q4 at two separate "V" Block 

Component Orientation: Q5 and Q8 (Intersection Point Q6/Q7)

Component Clamping: Against Resting

Operation 10 setup

As previously stated, if the fixture concept is feasible for two variants of components, if there is a significant difference in the component profile, managing the changed parts is difficult. Then, on the bottom face of the fixture plate, we must consider a separate setup for component 2.

Component type 1 is planned for the top face, with four components loaded. The component is loaded perpendicular to the X axis and parallel to the Z axis, with servo 4th axis rotation available. The component can be rotated to any position between 0 and 180 degrees.

Component type 2 is also planned for the bottom face, loading four components. The component is loaded perpendicular to the X axis and parallel to the Z axis, with servo 4th axis rotation available. The component can be rotated to any position between 0 and 180 degrees.

Component datum component 1 for Operation 20

Component Resting: On machined Front flange face 

Component Location: Flange Hole 1, dia.9.1

Component Orientation: Flange Hole 2, dia.9.1

Component Clamping: Against Resting

Component datum component 2

Component Resting: On machined Front flange face 

Component Location: Flange Hole 1, dia.9.1

Component Orientation: Flange Hole 2, dia.9.1

Operation 20 setup

Component type 1 is planned on the top face for the second operation, loading four components. The component is loaded perpendicular to the X axis and parallel to the Z axis, with servo 4th axis rotation available. The component can be rotated to any position between 0 and 180 degrees.

Component type 2 is also planned for the bottom face, loading four components. The component is loaded perpendicular to the X axis and parallel to the Z axis, with servo 4th axis rotation available. The component can be rotated to any position between 0 and 180 degrees.

To better understand the manufacturing process and cover the entire operation, including tool-specific factors, we have added an additional chapter. Only operating and machining parameters will be covered in the second chapter.

Click here to read Chapter 2>>>>

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