What is Horizontal machining center? Basic guide about - HMC machine

        When working with a simple block, face milling on a VMC (Vertical Machining Center) is straightforward. However, for side milling or milling on other planes of the cube, you need multiple setups for each plane operation, making the overall process time-consuming. In contrast, an HMC (Horizontal Machining Center) can handle side milling operations in a single setup.

Moreover, a VMC can only machine a single setup at a time. But with an HMC, the pallet changer allows you to set up multiple components while one operation is ongoing, significantly reducing setup time.

An HMC's structure is generally long and wide, with a larger tool magazine capacity. This design enables the machining of heavy and large components, allowing for multiple operations in a single setup.

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Horizontal Machining Center

What is Horizontal machining center?

• The HMC machine, a type of Column and Knee type milling machine, is renowned in the manufacturing industry for its heavy machining capacity. Known as the "Horizontal Machining Center" or "Horizontal Milling Machine," it offers numerous advantages.

• Structurally, the HMC differs from the VMC (Vertical Machining Center) in spindle orientation. The HMC's spindle is mounted horizontally, allowing it to machine heavy and large parts more efficiently than a VMC.
• Most HMC machines can operate synchronously in four different axes, making them ideal for multi-face machining.

Horizontal machining center Working principle

• The HMC machine is a type of column and knee milling machine that operates on the principle of a machining center. It removes material from the workpiece by rotating a cutter against it, with the cutter’s spindle either parallel to the worktable or perpendicular to its rotation axis.

• The HMC features three linear axes and one rotational axis, allowing it to remove material from all sides of a part, except the mounting side, and effectively expel chips from the cutting area.
• These axis movements and spindle rotations are controlled by an industrial CNC controller, often referred to as the "mind of the machine." This controller interprets the CNC program and commands the motors, spindles, and other machine components.
• Thanks to its four-axis movement and large tool magazine, the HMC can machine heavy and complex parts with fewer setups compared to a VMC machine.

Construction of HMC machine

• The entire HMC machine is built on a heavy and rigid base and column, made from Meehanite cast iron material. This material undergoes pre and post stress removal processes to increase strength, rigidity, and hardness. To avoid vibration and enhance other benefits, many companies use rigid structural parts combined with a "V" shaped rib reinforcement.

Explode video of HMC

• On this casting base, the X and Z axes of the HMC machine are mounted, while the Y axis is mounted on the column. For mass balancing in the Y axis, a "Dead" load system is used. The spindle in an HMC is mounted on the Y axis, compared to a VMC machine. All of these axes move via a linear motion (LM) and ballscrew arrangement.
• Other accessories, such as the ATC (Automatic Tool Changer) rack, pallet changer, chip evacuation system, lubrication system, coolant system, and electrical system, are mounted outside the base and column. Some of these components are also mounted on the HMC guard.

Axis designation in HMC machine

• In an HMC machine, four axes work synchronously: three linear axes and one rotational axis for multi-face machining. All these movements rely on linear motion (LM), LM blocks, and ball screws for precise movements.

X axis

• In an HMC machine, the X axis is responsible for moving the worktable front and back, where the workpiece is mounted. As previously discussed, this axis is mounted on the base and is also responsible for carrying the weight of the Z axis and the A axis (rotary axis). Therefore, the X axis is designed with heavy casting, and the motor required to rotate the ball screw is of high wattage.

Y axis

• In an HMC machine, the Y axis is responsible for the up and down movement of the spindle arrangement. Unlike in a VMC machine, where the Z axis handles the up and down movement of the spindle, in an HMC machine, this task is performed by the Y axis. The direction of the spindle axis rotation is parallel to the worktable, moving up and down.

Z axis

• In a VMC machine, the Z axis is responsible for the up and down movement of the spindle. However, in an HMC machine, the Z axis is responsible for the left and right movement of the worktable, on which the rotary axis and worktable are mounted.

A axis

• The A axis, or rotary axis, in an HMC machine enables machining on multiple faces with a single setup, eliminating the need for multiple setups required in a VMC machine. This makes HMC machines ideal for machining critical and complex parts.
• The A axis can rotate the worktable 360 degrees precisely, perpendicular to the spindle rotation axis. This feature offers several advantages, such as reduced setup time, easy referencing, and the ability to perform multi-face work efficiently.

Components of HMC machine

Base

• The HMC machine is a heavy and rigid structure designed for precise work. Its column and knee type structure is assembled on a casting base that supports the entire machine. This base bears the load of the machine, distributes it to the ground, and provides facilities to absorb vibrations, handle high cutting loads, and manage coolant flush.

Column

• In an HMC machine, the spindle is mounted on a vertical casting column and is capable of moving up and down along the column. To balance the counterweight, spindle accessories and the ATC (Automatic Tool Changer) mechanism are also mounted on the spindle.

Axis Mechanism

• The axes in a machining center play a crucial role in providing motion and carrying loads. Most HMC machines use an LM (linear motion) and ball screw mechanism. Key components of this mechanism include:

1. LM Guideways
2. LM Blocks
3. Ball Screws
4. Precision Nuts
5. Servo Motors
6. Couplings
7. Feedback Systems

• In this LM-ball screw mechanism, the LM guideways are complex-shaped rods on which the LM blocks slide linearly. The ball screw and precision nut mechanism convert the rotary motion of the motor into linear motion through threaded precision nuts.

Spindle

• The spindle in an HMC machine is responsible for rotating the cutter, which removes material from the workpiece. This rotational motion is powered by a high-torque motor connected to the spindle via a belt and pulley or gear mechanism. Various cutters, such as face mills, end mills, drill bits, boring bars, chamfer cutters, side mills, tapers, and reamers, are used for different milling purposes.

ATC Turret

• The ATC (Automatic Tool Changer) mechanism automates the tool change during a running program, reducing machining time. This is typically achieved using an umbrella, rack mechanism, or rotary-type mechanism that changes the tool from the spindle based on G-code and M-code commands.

Coolant Mechanism

• Due to high-speed operations and cutting forces, the spindle, cutter, and workpiece can become highly heated, potentially causing defects. To manage this, chilled coolant is continuously sprayed on the cutter. The coolant is pumped through a system that allows it to be reused multiple times.

Chip Conveyor Mechanism

• As the HMC machine removes metal, chips accumulate on the worktable, creating obstacles for machining. To address this, a chip conveyor mechanism is employed to remove chips from the machine and maintain a clear working area.

Advantages of HMC machine

Multi-Face Machining

• While a VMC machine can only work on a single face or plane during one setup, an HMC machine can handle up to five different faces or planes in a single setup due to its rotary table. This ability for multi-face machining is a crucial advantage of the HMC over the VMC.

Easy Alignment

• In a VMC machine, aligning a piece often requires manual adjustment, sometimes using a hammer, which can be imprecise. In contrast, an HMC machine simplifies alignment by rotating the worktable, making it easier to set the zero point accurately.

Setup Time Reduction

• With the capability to work on multiple planes from a single setup, the HMC significantly reduces the time required for clamping workpieces. Additionally, the availability of a pallet changer allows for easy setup of other pieces during ongoing operations, further saving time.

Accuracy & High Precision

• The HMC's LM-ball screw arrangement, heavy and rigid casting structure, vibration dampening system, and thermally stable inner components contribute to its ability to produce highly accurate and precise parts.

Heavy and Complex Parts Machining

• The heavy casting, column and knee type structure, and "V" shape rib reinforcement in HMC machines enable the machining of heavy parts with ease. The high RPM and heavy torque spindle also provide excellent surface finishing for complex geometries.

Lead Time Reduction

• An HMC typically features an automatic tool change rack with 100 to 200 tools and a pallet changer for multi-setup operations. Combined with multi-face machining capabilities, this reduces lead times compared to VMC machines.

Disadvantages of HMC Machine

Cost

• The major drawback of HMC machines is their high initial investment. The cost of components like the pallet changer, large castings, ATC racks, and heavy spindles makes the HMC approximately four times more expensive than a VMC.

Maintenance and Service

• The complex structure and expensive components of HMC machines lead to higher maintenance costs and increased complexity during servicing.

High Tool Cost

• The number of tools required for an HMC machine is greater than for a VMC, and the milling tools such as face mills, drills, boring bars, and taps are costlier.

Trained Workers Required

• Operating an HMC machine requires specialized skills and training, which can be difficult to find.

Miniature Parts Machining

• Due to the high cost of HMC machines, their overall cost per hour is higher than that of VMC machines. As a result, HMC machines are not ideal for manufacturing small or miniature parts but are well-suited for precision and complex parts.

Application of HMC machine

Manufacturing industry 

• In Manufacturing industry components Manufactured are highly precision and finishing of metal and non metals and for machining of this components,  HMC machine are widely used in manufacturing industry. 
• Parts like Casting piece, machineries components, single-double or multi assembly components are manufactured in HMC machine.

Die manufacturing:

• HMC is useful in complex die manufacturing, for example bottle, mask, hardware, glasses, injection molding etc mold die easily manufactured in hmc machine.

Automobile industry:

• Automotive parts are critical and complex in shape and it’s easily manufactured HMC machine. Cylinder head, crank case, gear box etc are manufactured in hmc machine.

Skills Required to Operate an HMC Machine

• To operate an HMC machine effectively, the following skills and knowledge are essential:

1. Understanding of engineering drawing and design
2. Ability to read mechanical drawings
3. Capability to set work offsets
4. Knowledge of various milling tools
5. Proficiency in tool offset and compensation
6. Experience with operating an HMC machine
7. Familiarity with technical machining parameters like feed rates and RPM
8. Proper understanding of length sign conversion

Conclusion

• HMC machine in which HMC stand for "Horizontal Machining Center" is types of column and knee milling machine and work on principle of milling machine.
• In HMC machine axis of spindle is horizontal or parallel two graound in which four axis namely X, Y, Z, A are worked synchonizely aganist rotating cutter or spindle in order to remove material from metal and non metals material.
• HMC has lots of advantages compare to VMC like Multi-Face Machining, Easy Alignment, Setup Time Reduction, Accuracy & High Precision, Heavy and Complex Parts Machining, Lead Time Reduction, but major disadvantage of HMC is Intial high cost.

Faqs

What does HMC stand for machine?

• HMC is called “Horizontal Machining Center” in CNC machine in which spindle are horizontally mounted about ground hence its called HMC.

What is a horizontal machining center?

• Horizontal machining center or HMC machine is the type of machining center in which rotating cutter moves against parts in order to remove material. In HMC machine cutter /spindle are mounted horizontally hence its called Horizontal machining center. 
•  HMC machine is work on concept of milling in order to remove material. In order to remove materials Rotating cutter moves against the linearly moves parts in three different directions and some feed and RPM. 
• HMC machine throws chips outside of workpiece hence chip evacuation is easy, also rotating table rotate work piece in order to work in multi faces.

What is the difference between CNC and HMC?

CNC machine: 

• In earlier days generally machine used in manufacturing industry are manually/hand operated or by punching card operated. After this invention is ongoing in Computerized operated machines and CNC machine came in market. General Definition of CNC machine is that ‘machine which operated automatically by giving some commands to computer and computer can perform whole operation is called CNC machine’. 
• After the introduction of this things, for process like milling , turning, cutting, drilling etc. Separate machine are manufactured which operated by computer. For example CNC mill, CNC turning, CNC laser cutting, CNC router, CNC bending etc. Are used for cutting materials metal, non metals. 

HMC machine: 

• HMC machine is one types of CNC machine in which Milling work done in order to remove material from metal and non metal materials. In HMC 4 axis synchronously work and spindle mounted horizontally hence its called Horizontal machining center.

How many axis are in an HMC machine?

• HMC machine are having 4 axis which synchronously move with each other for machining, out of that 3 axis are moves linearly, where one is move in rotation..
• X axis: which moves mounted workpiece front and back by LM and ball screw arrangement.
• Y axis: this axis lead the motion of workpiece/worktable up and down.
• Z axis: z axis in HMC machine are linearly handle the workpiece in left right direction.
• A axis: where A axis in HMC are additional axis for rotary movement of workpiece and this axis of rotation are perpendicular to spindle rotation axis.

Why should you buy a horizontal machining center?

• Horizontal machining center has lots of advantages out of CNC machining center machinery and because of that reason HMC is used in most of industry.

1. Due to additional components and accessories like pallet changer, High ATC capacity, 4th rotary axis can produce machining component in less time with greater accuracy.
2. Structure of HMC is heavy and rigid cast structure by which great surface finishing achieved and also reduce vibration.
3. By mounting in single face you can able to machine in 5 other face in multiple plane for which in VMC you have to setup piece multiple time.
4. Operation like milling, drilling, boring, pocketing, grooving, contouring, facing, taping etc can done easily.

What are some additional costs of adding a horizontal machining center?

• Compare to VMC machine HMC are costlier due to use of additional components uses.

1. Automatic Tool Change rack used in HMC machine is upto 100 tool capacity and cost of pneumatic, sensor which used to handle ATC are costlier.
2. Pallet changer, which specially used in HMC machine are used in HMC to reduce setup time, which further affect the price of HMC machine.
3. Rotary table which helpful to rotate work piece 360 around spindle, for which high KW motor required with special mechanism which also affect initial price of HMC machine.

Which company is best for HMC machines?