Mitsui Seiki Horizontal Machining Centers

Mitsui Seiki HS6A

$800,000 - $1,200,000 Updated 2026-03-16

Key Specifications

X Travel

900 mm (35.4 in)

Y Travel

850 mm (33.5 in)

Z Travel

950 mm (37.4 in)

Spindle Taper

No. 50 (CAT50 / BT50 / HSK-A100)

Tool Capacity

60 (standard) / 120 (optional magazine)

Rapid Traverse

40 m/min (1,575 ipm) all axes

Overview

The Mitsui Seiki HS6A is an ultra-precision 630 mm pallet horizontal machining center built for manufacturers where tenths-of-a-micron repeatability is a non-negotiable requirement. Mitsui Seiki has produced precision HMCs from their Kiyohara factory in Tochigi, Japan, for over 70 years, and the HS6A represents the apex of their horizontal platform. The machine is used extensively in aerospace, defense, semiconductor equipment, and precision mold applications where standard HMC accuracy is simply insufficient.

The HS6A is built on a Meehanite cast iron base with full thermal compensation — oil-cooled spindle, ballscrew cooling, and ambient temperature-compensated linear scale feedback on all axes. Positioning accuracy reaches ±0.001 mm full stroke with repeatability of ±0.0005 mm, verified by laser interferometry on every machine before shipment. These are guaranteed specifications, not typical values.

The 630 mm pallet accommodates workpieces up to 1,000 mm diameter and 1,250 mm tall. X/Y/Z travels of 900 x 850 x 950 mm provide generous work envelopes for complex prismatic parts. The 6,000 RPM, 30 kW (40 hp) inline-direct spindle handles heavy steel and titanium cutting with rigid taper (No. 50) tooling. A 60-tool ATC and dual-station APC are standard. The B-axis rotary table indexes at 0.001° resolution.

The HS6A competes with the Makino a81nx, Heller H 5000, and Okuma MA-600H, but targets a narrower, more demanding segment of users who cannot tolerate thermal drift or positional uncertainty. For semiconductor equipment, defense optics mounts, and turbine blade fixtures, the HS6A is a reference-grade machine.

Full Specifications

Parameter	Value
Pallet Size	630 mm (24.8 in)
X-Axis Travel	900 mm (35.4 in)
Y-Axis Travel	850 mm (33.5 in)
Z-Axis Travel	950 mm (37.4 in)
Max Workpiece Diameter	1,000 mm (39.4 in)
Max Workpiece Height	1,250 mm (49.2 in)
Max Workpiece Weight	4,400
Spindle Taper	No. 50 (CAT50 / BT50 / HSK-A100)
Spindle Speed	6,000 RPM (standard) / 10,000 RPM (optional)
Spindle Motor Power	30 kW (40 hp) continuous / 37 kW (50 hp) 30-min
Spindle Torque	1,432 Nm (1,056 ft-lb) at low range
Rapid Traverse Rate	40 m/min (1,575 ipm) all axes
Feed Rate	1–20,000 mm/min
Positioning Accuracy	±0.001 mm (±0.00004 in) full stroke
Repeatability	±0.0005 mm (±0.00002 in)
Rotary Table Resolution	0.001°
Feedback	Full-closed loop, linear scales + rotary encoders on all axes
Thermal Compensation	Spindle oil cooling, ballscrew cooling, ambient temperature compensation
Tool Capacity	60 (standard) / 120 (optional magazine)
Tool Change Time	3.5 sec (chip-to-chip)
Pallet Changer	2-station APC (standard)
Pallet Change Time	18 sec
Way Type	Box ways (X, Y, Z) — induction hardened and precision-ground
Base Material	Meehanite cast iron, stress-relieved
CNC Control	FANUC 31i-B5
Machine Weight	22,000 kg (48,500 lb)
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Machine Type	Machining Center
Num Of Axes	5
Operation Type	CNC
Cnc Brand	Fanuc 15M
Table Size L X W	39.300(L) x 39.300(W)
Support Index Table	Standard
Support Rotary Table	Optional
Direction	Horizontal
Taper	# 50
Top Rpm	4,500
Top Rpm Opt	10,000
Hp	20.00
Tool Carrier	ATC
Num Tools	32
Num Tools Opt	270
Tool Change Chip Time	12.00
Pallet Changer Available	Optional
Num Pallets	2
Num Pallets Opt	10
Num Axes	5
U Axis	None
X1	51.180"
Y1	47.240"
Z1	39.700"
A1	120.000°
B1	360.000°

Specifications sourced from techspex.com — verified 2026-03-28

Strengths & Limitations

Strengths

Laser-verified ±0.001 mm positioning accuracy guaranteed on every machine — not a catalog spec but a shipped certificate
Full thermal compensation system (spindle oil cooling, ballscrew cooling, ambient temp correction) minimizes thermal drift during long production runs
Meehanite cast iron box way construction provides exceptional vibration damping for superior surface finishes in steel and titanium
No. 50 taper spindle delivers massive torque for heavy material removal in aerospace alloys and hardened steels
60–120 tool capacity with 3.5-second chip-to-chip ATC supports complex multi-operation aerospace and defense parts
Built at Mitsui Seiki's Kiyohara factory under rigorous quality control — one of the most respected precision machine tool builders in Japan

Limitations

Price of $800K–$1.2M places this in a rarified market segment; ROI requires consistent high-value precision work
6,000 RPM base spindle speed is not suited for high-speed aluminum or composites — higher RPM spindle option adds cost
Mitsui Seiki has limited dealer presence outside Japan and the United States; support can be slow in other regions
40 m/min rapids are adequate but lag behind linear-guide competitors running 60 m/min — chip-to-chip time is not a strength
Long lead times (typically 6–12 months) are common for configured machines due to Kiyohara factory capacity

Best For

Aerospace structural component manufacturers requiring certified dimensional accuracy on titanium and aluminum alloy parts Defense contractors producing precision mounts, housings, and optical structures where micron-level tolerances are specified Semiconductor equipment builders machining precision frames, stages, and vacuum components to sub-micron flatness Precision mold shops requiring guaranteed positional accuracy across full stroke for complex multi-cavity tooling Medical device manufacturers producing implant fixtures, surgical instrument components, and orthopedic guides

Frequently Asked Questions

01 What is the difference between the Mitsui Seiki HS6A and the HS5A?

The HS6A uses a 630 mm pallet while the HS5A uses a 500 mm pallet. The HS6A has larger X/Y/Z travels (900 x 850 x 950 mm vs 800 x 700 x 850 mm) and a higher maximum workpiece weight. Both share the same thermal compensation architecture and ±0.001 mm guaranteed positioning accuracy. Choose the HS6A for larger prismatic parts; the HS5A for smaller, higher-mix work.

02 How does Mitsui Seiki guarantee ±0.001 mm positioning accuracy?

Every HS6A undergoes laser interferometry calibration at the Kiyohara factory before shipment. The machine is built with full-closed-loop feedback using linear scales on all axes, oil-cooled spindle and ballscrews to minimize thermal growth, and ambient temperature compensation in the control. The calibration certificate specifying measured accuracy at multiple positions along each axis ships with the machine.

03 Is the HS6A compatible with FANUC or Siemens controls?

The HS6A is typically configured with FANUC 31i-B5, which supports 5-axis simultaneous interpolation, advanced thermal compensation cycles, and high-speed look-ahead for contouring. Siemens 840D sl is available as an option for customers with established Siemens programming environments. Both controls support the full precision feature set of the machine.

04 What pallet automation options are available?

The standard 2-station APC can be expanded with Mitsui Seiki's multi-pallet stocker systems for lights-out production. Pallet pools of 4, 8, and 16 stations are available. The B-axis table accommodates custom tombstone fixturing for multi-face machining, which is common in aerospace bulk head and structural component work.

05 How does the HS6A compare to the Makino a81nx for aerospace work?

The Makino a81nx is a high-speed, linear-guide HMC optimized for aluminum aerospace structures with a 14,000 RPM spindle and 60 m/min rapids. The Mitsui Seiki HS6A targets titanium, steel, and high-precision mixed-material work with box ways, a torque-heavy No. 50 spindle, and guaranteed ±0.001 mm positioning. The Makino wins on throughput for aluminum; the Mitsui Seiki wins on absolute accuracy and thermal stability.